Glossary

1.3 Chemical Principles in Environmental Systems

4 min read•august 1, 2024

Chemical principles shape how substances behave in the environment. and kinetics govern reactions, while equilibria determine distribution. These concepts explain processes like photosynthesis, ocean acidification, and ozone depletion.

affects how chemicals move and interact in ecosystems. Understanding properties like and helps predict environmental fate. This knowledge is crucial for assessing risks and developing strategies to address pollution and environmental challenges.

Chemical Principles in Environmental Systems

Thermodynamics in Environmental Systems

Top images from around the web for Thermodynamics in Environmental Systems

  • Free Energy | Chemistry View original

    Is this image relevant?

  • Gibbs Free Energy View original

    Is this image relevant?

  • Free Energy | Chemistry View original

    Is this image relevant?

1 of 3

Top images from around the web for Thermodynamics in Environmental Systems

  • Free Energy | Chemistry View original

    Is this image relevant?

  • Gibbs Free Energy View original

    Is this image relevant?

  • Free Energy | Chemistry View original

    Is this image relevant?

1 of 3
  • Thermodynamics governs chemical reaction direction and extent in environmental systems focusing on , , and changes
  • First and second laws of thermodynamics explain energy transformations and process spontaneity in the environment
    • First law demonstrates energy conservation (energy cannot be created or destroyed)
    • Second law describes increasing entropy in spontaneous processes
  • Gibbs free energy (ΔG\Delta G) determines reaction spontaneity
    • Spontaneous reactions have negative ΔG\Delta G values
    • ΔG=ΔH−TΔS\Delta G = \Delta H - T\Delta S relates enthalpy (ΔH\Delta H) and entropy (ΔS\Delta S) changes
  • Environmental examples of thermodynamic principles
    • Photosynthesis (endergonic process requiring energy input)
    • Combustion of fossil fuels (exergonic process releasing energy)

Chemical Kinetics in Environmental Processes

  • describes in environmental systems influenced by temperature, concentration, and catalysts
  • relates reaction rate constants to temperature
    • k=Ae−Ea/RTk = Ae^{-E_a/RT} where kk is the rate constant, AA is the pre-exponential factor, EaE_a is , RR is the gas constant, and TT is temperature
  • Activation energy concepts explain energy barriers for chemical reactions in environmental processes
    • Catalysts lower activation energy, accelerating reactions (enzymatic processes in ecosystems)
  • including rate-determining steps and intermediate species explain complex environmental reactions
    • Ozone depletion in the stratosphere involves multiple steps with different rates
  • Steady-state and equilibrium approximations simplify analysis of environmental chemical systems
    • Steady-state applied to atmospheric pollutants with constant emission and removal rates

Chemical Reactions in Environmental Processes

Equilibria in Environmental Systems

  • determine substance distribution and speciation in air, water, and soil systems
  • explains environmental system responses to concentration, temperature, and pressure changes
    • Increased CO2 in the atmosphere shifts carbonate equilibrium in oceans, leading to acidification
  • fundamental to pH variations in natural waters, soil chemistry, and atmospheric processes
    • \ceH2O<=>H++OH−\ce{H2O <=> H+ + OH-} water self-ionization equilibrium
    • Carbonic acid system in natural waters: \ceCO2+H2O<=>H2CO3<=>HCO3−+H+<=>CO32−+2H+\ce{CO2 + H2O <=> H2CO3 <=> HCO3- + H+ <=> CO3^2- + 2H+}
  • and equilibria critical in biogeochemical cycles (aquatic and soil environments)
    • Nitrogen cycle: nitrification and denitrification processes
    • Iron oxidation and reduction in soils affecting nutrient availability

Complex Environmental Reactions

  • influence trace metal mobility and bioavailability in environmental systems
    • Formation of metal-organic complexes in soil solutions
  • Precipitation and govern mineral formation and dissolution, affecting water hardness and soil composition
    • Calcium carbonate precipitation in hard water: \ceCa2++CO32−<=>CaCO3(s)\ce{Ca^2+ + CO3^2- <=> CaCO3 (s)}
  • described by essential for volatile compound between air and water
    • Dissolved oxygen in water bodies: \ceO2(g)<=>O2(aq)\ce{O2 (g) <=> O2 (aq)}
    • Atmospheric pollutant dissolution in raindrops (acid rain formation)

Chemical Speciation and Pollutant Fate

Fundamentals of Chemical Speciation

  • distributes elements among different chemical forms in a system, affecting reactivity, toxicity, and environmental fate
  • of weak acids and bases influences mobility and bioavailability in aquatic and soil environments
    • Ammonia/ammonium equilibrium: \ceNH3+H2O<=>NH4++OH−\ce{NH3 + H2O <=> NH4+ + OH-}
  • including free ions, complexes, and organometallic compounds determines heavy metal toxicity and in ecosystems
    • Mercury speciation: elemental Hg, inorganic Hg2+, and organic methylmercury
  • of elements with multiple oxidation states affects solubility and environmental behavior
    • Arsenic speciation: As(III) more toxic and mobile than As(V)

Speciation Analysis and Environmental Impact

  • including ionization and complexation influences , , and transport in environmental media
    • Polycyclic aromatic hydrocarbons (PAHs) partitioning between dissolved and particulate phases
  • Speciation modeling tools and techniques essential for predicting pollutant behavior in complex environmental systems
    • Chemical equilibrium models (MINTEQ, PHREEQC)
    • Spectroscopic methods (X-ray absorption spectroscopy, NMR)
  • concept emphasizes speciation importance in risk assessment and remediation strategies
    • Bioavailable fraction of soil contaminants for plant uptake
    • Dissolved vs. particulate-bound pollutants in aquatic ecosystems

Chemical Properties and Environmental Transport

Solubility and Partitioning in Environmental Systems

  • Solubility governs chemical partitioning between aqueous and solid phases, affecting mobility in soil and water systems
  • (Kow) predicts organic compound environmental fate
    • Kow=[solute]octanol[solute]waterK_{ow} = \frac{[solute]_{octanol}}{[solute]_{water}}
    • High Kow indicates hydrophobicity and potential for bioaccumulation
  • Salting-out effects and co-solvent phenomena alter compound solubility in natural waters
    • Decreased solubility of organic pollutants in seawater compared to freshwater
  • (adsorption and absorption) affect chemical retention and mobility in soils and sediments
  • Soil organic carbon-water partitioning coefficient (Koc) estimates organic contaminant sorption behavior in soils
    • Koc=[solute]soilorganiccarbon[solute]waterK_{oc} = \frac{[solute]_{soil organic carbon}}{[solute]_{water}}

Volatility and Environmental Distribution

  • Volatility expressed as determines chemical partitioning into gas phase, influencing atmospheric transport and deposition
  • Henry's law constant relates air-water partitioning of volatile organic compounds (VOCs)
    • KH=[compound]air[compound]waterK_H = \frac{[compound]_{air}}{[compound]_{water}}
    • Important for understanding VOC fate in the environment (groundwater contamination, air pollution)
  • , bioaccumulation, and processes influenced by chemical properties lead to pollutant accumulation in organisms and food chains
    • DDT accumulation in aquatic food webs
  • Chemical structure and properties relate to persistence and degradation, affecting long-term fate and ecological impact
    • Halogenated compounds (PCBs, dioxins) highly persistent due to strong carbon-halogen bonds
  • Transport mechanisms (, , ) influenced by pollutant chemical properties and environmental conditions
    • Groundwater contaminant plume movement
  • incorporate chemical property data to predict pollutant distribution across environmental compartments
    • Fugacity models for predicting chemical partitioning between air, water, soil, and biota

Key Terms to Review (43)

Acid-base equilibria: Acid-base equilibria refer to the dynamic balance between acids and bases in a solution, characterized by the transfer of protons (H\(^+\)) according to the Bronsted-Lowry theory. This concept is crucial for understanding how various chemical species interact in environmental systems, influencing pH levels, chemical reactivity, and the behavior of pollutants in aquatic environments.
Activation energy: Activation energy is the minimum amount of energy required for a chemical reaction to occur. It plays a crucial role in determining the rate at which reactions happen, influencing how quickly substances can interact and transform into products. Understanding activation energy helps in studying reaction mechanisms and the effects of environmental factors on these reactions.
Advection: Advection is the process by which heat or matter is transported from one place to another by the bulk movement of a fluid, such as air or water. This mechanism is crucial in environmental systems, as it helps distribute pollutants, nutrients, and thermal energy within the atmosphere and hydrosphere, impacting weather patterns and ecological health.
Arrhenius Equation: The Arrhenius equation is a mathematical formula that describes the temperature dependence of reaction rates, expressed as $$k = A e^{-\frac{E_a}{RT}}$$, where $$k$$ is the rate constant, $$A$$ is the pre-exponential factor, $$E_a$$ is the activation energy, $$R$$ is the universal gas constant, and $$T$$ is the temperature in Kelvin. This equation illustrates how increasing temperature can accelerate chemical reactions, which has significant implications in various environmental systems, such as pollutant degradation and biochemical processes.
Bioaccumulation: Bioaccumulation refers to the process by which living organisms accumulate toxic substances, such as heavy metals or persistent organic pollutants, from their environment at a rate faster than they can eliminate them. This leads to increasing concentrations of these harmful substances within an organism over time, impacting its health and the health of organisms higher in the food chain. Understanding bioaccumulation is crucial for assessing environmental pollution, especially in relation to water and soil contaminants.
Bioavailable fraction: The bioavailable fraction refers to the portion of a substance, such as a pollutant or nutrient, that is readily accessible for uptake by organisms in the environment. This concept is crucial as it helps to understand how different chemicals interact with living organisms and their potential effects on ecosystems. Factors like solubility, chemical form, and environmental conditions significantly influence the bioavailable fraction, impacting how organisms absorb these substances.
Bioconcentration: Bioconcentration is the process by which certain substances, often toxic chemicals, accumulate in an organism's tissues at higher concentrations than those found in the surrounding environment. This phenomenon is crucial for understanding how pollutants move through ecosystems and can have significant impacts on food webs and human health. It typically occurs in aquatic organisms, where contaminants are taken up from water through gills or skin and stored in fatty tissues.
Biomagnification: Biomagnification is the process by which the concentration of toxic substances increases as they move up the food chain, affecting organisms at higher trophic levels. This phenomenon occurs because certain pollutants, such as heavy metals and persistent organic pollutants, are not easily broken down or excreted by living organisms, leading to higher concentrations in predators. Understanding biomagnification is crucial in analyzing soil pollution, interpreting environmental data, and applying chemical principles to environmental systems.
Chemical equilibria: Chemical equilibria refer to the state in a chemical reaction where the concentrations of reactants and products remain constant over time, indicating that the forward and reverse reactions occur at the same rate. This dynamic balance is crucial for understanding how reactions behave in environmental systems, where various factors can shift the equilibrium position and influence chemical processes.
Chemical kinetics: Chemical kinetics is the branch of chemistry that studies the rates of chemical reactions and the factors that influence these rates. Understanding chemical kinetics is crucial for predicting how fast a reaction will occur, which has direct implications for environmental processes such as pollutant degradation, atmospheric reactions, and biochemical transformations.
Chemical speciation: Chemical speciation is the process of identifying and quantifying the different forms of a chemical element or compound in a given environment. This concept is vital for understanding how various chemical species behave, interact, and transform within environmental systems, influencing factors like bioavailability, toxicity, and chemical reactivity.
Complexation reactions: Complexation reactions involve the formation of a complex between a metal ion and one or more ligands, resulting in a new chemical species. These reactions play a crucial role in environmental chemistry as they influence the behavior, mobility, and bioavailability of metals in natural systems. Understanding these reactions is essential for assessing the impact of metals on ecosystems and developing remediation strategies for contaminated environments.
Degradation: Degradation refers to the process by which substances break down into simpler compounds or elements due to biological, chemical, or physical actions. This phenomenon is crucial in understanding how pollutants behave in the environment, their persistence, and their potential impacts on ecosystems. Degradation plays a significant role in the fate and transport of contaminants in soil, influencing how they move, persist, and ultimately affect soil health and function.
Diffusion: Diffusion is the process through which particles spread from areas of higher concentration to areas of lower concentration, driven by the random motion of molecules. This natural movement occurs in gases, liquids, and solids and plays a crucial role in various environmental processes, including the fate and transport of pollutants in different systems. Understanding diffusion helps explain how substances interact and move within environmental contexts, impacting pollution levels and chemical reactions.
Dispersion: Dispersion refers to the process by which particles or substances spread out and become distributed throughout a medium, often in the context of environmental systems. This phenomenon plays a crucial role in understanding how pollutants move through air, water, and soil, influencing their availability and impact on ecosystems. The rates and mechanisms of dispersion can vary widely depending on factors such as the properties of the substances involved, environmental conditions, and interactions with other materials.
Dissolution equilibria: Dissolution equilibria refers to the state of balance achieved when a solid solute dissolves in a solvent to form a solution, where the rate of dissolution equals the rate of crystallization. This concept is crucial for understanding how substances interact within environmental systems, as it helps explain processes such as the transport and availability of nutrients, pollutants, and minerals in various water bodies. It highlights the importance of factors like temperature, pressure, and concentration in determining the solubility of compounds in natural environments.
Enthalpy: Enthalpy is a thermodynamic quantity that represents the total heat content of a system at constant pressure, defined as the sum of the internal energy and the product of pressure and volume. It is essential for understanding how energy is transferred in chemical reactions and physical processes, particularly in environmental contexts where reactions may release or absorb heat, influencing ecosystems and climate. Enthalpy changes provide insights into reaction spontaneity and help predict the behavior of substances during phase changes.
Entropy: Entropy is a measure of the disorder or randomness in a system, often associated with the second law of thermodynamics. In environmental systems, entropy helps us understand how energy transformations impact the availability and quality of resources. As systems become more disordered, energy becomes less useful for doing work, which is crucial in assessing ecological processes and chemical reactions in the environment.
First law of thermodynamics: The first law of thermodynamics states that energy cannot be created or destroyed, only transformed from one form to another. This principle is foundational in understanding how energy flows through environmental systems, impacting chemical reactions, heat exchanges, and the behavior of matter in various states.
Gas-liquid equilibria: Gas-liquid equilibria refers to the state of balance between the gas phase and the liquid phase of a substance, where the rate of molecules escaping from the liquid to the gas equals the rate of molecules condensing from the gas back to the liquid. This concept is crucial in understanding how gases dissolve in liquids and is fundamental to various chemical processes and environmental systems, particularly in understanding pollutant behavior and transport in natural water bodies.
Gibbs Free Energy: Gibbs Free Energy (G) is a thermodynamic potential that measures the maximum reversible work obtainable from a thermodynamic system at constant temperature and pressure. It combines the system's enthalpy (H) and entropy (S) into a single value, represented by the equation G = H - TS, where T is the temperature in Kelvin. This concept is essential in predicting the spontaneity of chemical reactions and understanding energy transformations in environmental systems.
Henry's Law: Henry's Law states that at a constant temperature, the amount of gas that dissolves in a liquid is directly proportional to the partial pressure of that gas above the liquid. This principle is fundamental in understanding how gases behave in natural water bodies, including oceans and lakes, and their interactions with the atmosphere.
Le Chatelier's Principle: Le Chatelier's Principle states that if a system at equilibrium is subjected to a change in concentration, temperature, or pressure, the system will adjust itself to counteract that change and restore a new equilibrium. This principle helps explain how chemical reactions behave in environmental systems, where various factors can influence the concentrations of reactants and products, affecting processes such as pollution degradation and natural cycles.
Metal speciation: Metal speciation refers to the distribution and chemical forms of metals in the environment, which can vary significantly depending on factors such as pH, temperature, and the presence of complexing agents. Understanding metal speciation is crucial because it influences metal bioavailability, toxicity, and movement through ecosystems. Different species of metals can exhibit varying degrees of reactivity and interaction with biological organisms, thereby affecting their environmental impact.
Multimedia environmental models: Multimedia environmental models are computational tools that simulate the transport, transformation, and fate of pollutants across different environmental media, such as air, water, and soil. These models integrate data from various sources to assess the interactions between different environmental compartments and predict how chemicals behave in the environment. By analyzing these interactions, these models help in understanding the impact of pollutants on ecosystems and human health.
Octanol-water partition coefficient: The octanol-water partition coefficient, often represented as KOW, quantifies the distribution of a chemical compound between an organic solvent (octanol) and water. This coefficient is essential for understanding how pollutants interact within the environment, predicting their bioavailability, mobility, and potential for bioaccumulation in aquatic organisms.
Organic pollutant speciation: Organic pollutant speciation refers to the identification and characterization of different forms or species of organic pollutants in environmental systems. Understanding speciation is crucial because it affects the behavior, reactivity, and toxicity of these pollutants in air, water, and soil. The speciation of organic pollutants can provide insights into their sources, transformation processes, and potential impacts on ecosystems and human health.
Partitioning: Partitioning refers to the process by which a chemical substance distributes itself between two or more phases, such as air, water, and soil. This concept is crucial in understanding how pollutants behave in the environment, influencing their transport, transformation, and potential impact on ecosystems and human health. Different chemical properties, like solubility and volatility, play a significant role in determining how a substance partitions, which can affect its bioavailability and persistence in various environmental compartments.
Persistence: Persistence refers to the continued presence of a chemical in the environment, often resulting from its resistance to degradation processes. Chemicals that exhibit high persistence can remain in ecosystems for extended periods, leading to potential accumulation and adverse effects on living organisms. Understanding persistence is crucial when evaluating the environmental impact of various substances and how they interact within ecological systems.
PH-dependent speciation: pH-dependent speciation refers to the way in which the chemical forms or species of an element, particularly metals and nutrients, change with the pH of the surrounding environment. This is crucial in understanding how substances behave in aquatic and terrestrial systems, as the availability and toxicity of these species can vary significantly across different pH levels. For example, certain metals may exist as soluble ions at low pH but precipitate as solid forms at higher pH, influencing their mobility and bioavailability in ecosystems.
Precipitation equilibria: Precipitation equilibria refers to the balance between the rates of dissolution and precipitation of a solute in a saturated solution, which determines whether a substance will remain dissolved or form solid particles. This concept is crucial in understanding how chemical substances behave in natural waters, where various factors such as temperature, pH, and ionic strength can influence the solubility of compounds and their tendency to precipitate.
Reaction mechanisms: Reaction mechanisms are the step-by-step processes through which chemical reactions occur, detailing the individual steps and the transformation of reactants into products. Understanding these mechanisms helps to illustrate how different factors, such as concentration and temperature, influence the rate of a reaction and the pathways that different chemicals take. They are crucial in environmental chemistry for predicting how pollutants break down or transform in various systems.
Reaction Rates: Reaction rates refer to the speed at which reactants are converted into products in a chemical reaction. These rates can be influenced by various factors, including concentration, temperature, and the presence of catalysts. Understanding reaction rates is crucial for predicting how long it will take for certain reactions to occur, especially in environmental contexts where these reactions play a significant role in atmospheric chemistry and environmental systems.
Redox reactions: Redox reactions, short for reduction-oxidation reactions, are chemical processes in which the oxidation states of atoms are changed through the transfer of electrons. These reactions are crucial in various environmental processes, such as the cycling of elements and energy transformations in ecosystems, impacting everything from soil chemistry to atmospheric composition.
Redox speciation: Redox speciation refers to the distribution of different chemical species in a system based on their oxidation states and redox potentials. This concept is crucial for understanding how various forms of elements, such as metals, can exist in different oxidation states and how these states influence chemical reactivity, mobility, and bioavailability in environmental systems.
Second law of thermodynamics: The second law of thermodynamics states that the total entropy of an isolated system can never decrease over time, and it tends to increase, leading to the inevitable dissipation of energy. This principle has significant implications in various processes, particularly in how energy transformations occur in the environment and influences the efficiency of biological and chemical systems.
Solubility: Solubility is the ability of a substance (the solute) to dissolve in a solvent, resulting in a homogeneous solution. This property is crucial in environmental systems because it influences the distribution and movement of pollutants, nutrients, and minerals in water bodies, soil, and atmospheric conditions.
Sorption processes: Sorption processes refer to the physical and chemical mechanisms by which one substance becomes attached to another, encompassing both adsorption and absorption. These processes are critical in understanding how contaminants interact with environmental media, influencing their transport, bioavailability, and overall environmental fate.
Speciation: Speciation is the evolutionary process through which new biological species arise from existing ones, often driven by genetic, ecological, and behavioral factors. It plays a critical role in the biodiversity of ecosystems, as it can influence the distribution of species and their interactions within various environmental contexts. Understanding speciation helps illuminate how organisms adapt and evolve in response to changing environmental conditions.
Steady-state approximation: The steady-state approximation is a simplification used in chemical kinetics where the concentration of intermediates remains constant over time during a reaction. This means that the rate of formation of an intermediate equals its rate of consumption, leading to a dynamic equilibrium where the concentrations do not change significantly. This concept is particularly useful for analyzing complex reactions in environmental systems, where understanding the behavior of transient species is essential.
Thermodynamics: Thermodynamics is the branch of physics that deals with the relationships between heat, work, temperature, and energy. It plays a crucial role in understanding how energy transformations occur in natural systems, influencing chemical reactions and processes in the environment. By studying thermodynamics, we gain insight into energy conservation, spontaneity of reactions, and the overall behavior of matter in different states.
Vapor Pressure: Vapor pressure is the pressure exerted by a vapor in thermodynamic equilibrium with its liquid or solid form at a given temperature. It is an important property that helps determine how substances behave in various environmental conditions, influencing processes such as evaporation and condensation, which are key to understanding the physical and chemical properties of water and their implications in environmental systems.
Volatility: Volatility refers to the tendency of a substance to vaporize or transition from a liquid or solid state to a gas at a given temperature and pressure. It is a critical factor in understanding how chemicals behave in environmental systems, influencing processes such as evaporation, air pollution, and the transport of pollutants in the atmosphere. High volatility means that a substance readily escapes into the air, while low volatility indicates that it remains more stable in its liquid or solid form.
© 2024 Fiveable Inc. All rights reserved.
AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.
Back
Practice QuizGlossary
Practice QuizGlossary
Next guide