5.2 Calorimetry
3 min read•june 24, 2024
is all about measuring heat transfer during chemical reactions or physical processes. It's based on the idea that energy is conserved, so the heat released or absorbed by a equals the heat absorbed or released by its .
To measure heat transfer, we use calorimeters. These devices monitor temperature changes in a known amount of substance, usually water. By calculating the heat change, we can determine the energy involved in reactions, which is crucial for understanding .
Calorimetry
Heat transfer measurement in calorimetry
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- measures heat transfer during chemical reactions or physical processes based on conservation of energy principle
- Heat released or absorbed by system equals heat absorbed or released by surroundings
- Monitors temperature change in known amount of substance (water) in
- Substance undergoing temperature change called 's contents
- Temperature change of calorimeter's contents proportional to heat transferred during reaction or process
- Proportionality constant is of calorimeter's contents
- Must consider heat capacity of calorimeter itself in calculations
- Known as or heat capacity of calorimeter
Calculations with calorimetry data
- Calculate heat change using equation:
- : heat energy transferred (J)
- : mass of substance (g)
- : of substance (J/g°C)
- : change in temperature (°C)
- Specific heat capacity: amount of heat required to raise temperature of 1 g of substance by 1°C
- Unique to each substance, found in reference tables
- When using calorimeter, heat change equation becomes:
- : heat change of calorimeter's contents
- : heat change of calorimeter itself
- : calorimeter constant (J/°C)
- In calorimetry experiment, heat lost by system equals heat gained by surroundings (calorimeter and contents), assuming no heat lost to environment
- Represented by equation:
- This principle is based on the law of in
Types of calorimeters and applications
- Two main types: constant-pressure calorimeters and bomb calorimeters
- Constant-pressure calorimeters (coffee-cup calorimeters) operate at constant pressure (usually atmospheric)
- Measure heat changes in reactions not involving gases or producing gases at low pressures
- Examples: measuring , neutralization, combustion of food or fuel samples
- Simple and inexpensive but less precise than bomb calorimeters
- Bomb calorimeters operate at constant volume, measure heat changes in combustion reactions
- Reaction takes place inside sealed, pressurized "bomb" filled with oxygen
- Bomb submerged in known amount of water inside insulated container
- More precise than constant-pressure calorimeters, can measure of solids, liquids, and gases
- More expensive and complex to use than constant-pressure calorimeters
- Designed to maintain an , minimizing heat exchange with the surroundings
Thermal Equilibrium and Energy Transfer
- Calorimetry relies on the principle of between the system and surroundings
- Heat flows from higher temperature regions to lower temperature regions until thermal equilibrium is reached
- The total energy of the system and surroundings remains constant, demonstrating energy conservation
- Accurate measurements in calorimetry depend on achieving and maintaining thermal equilibrium
Key Terms to Review (33)
Adiabatic Process: An adiabatic process is a thermodynamic change in a system in which there is no transfer of heat or mass between the system and its surroundings. This means that the system neither gains nor loses energy through heating or cooling, and all changes in the system's energy are due to work done on or by the system.
Bomb calorimeter: A bomb calorimeter is a device used to measure the heat of combustion of a sample. It operates at constant volume and provides precise measurements of energy changes in chemical reactions.
Bomb Calorimeter: A bomb calorimeter is an instrument used to measure the heat of combustion, or the amount of heat released during the complete burning of a sample. It is a crucial tool in the field of calorimetry, which is the study of heat transfer and energy changes in chemical reactions and physical transformations.
Calorie: A calorie is a unit of measurement that quantifies the amount of energy stored in food or released during the body's metabolic processes. It represents the energy required to raise the temperature of one gram of water by one degree Celsius.
Calorimeter: A calorimeter is an instrument used to measure the amount of heat absorbed or released during a chemical or physical process. It helps determine the enthalpy changes in reactions.
Calorimeter: A calorimeter is a device used to measure the amount of heat energy released or absorbed during a chemical or physical process. It provides a way to quantify the energy changes that occur in a system, allowing for the study of thermochemical reactions and properties.
Calorimeter Constant: The calorimeter constant, also known as the calorimeter heat capacity, is a measure of the heat capacity of a calorimeter. It represents the amount of energy required to raise the temperature of the calorimeter by one degree Celsius. This constant is a crucial parameter in calorimetry, the study of heat transfer in chemical and physical processes.
Calorimetry: Calorimetry is the measurement of heat transfer in chemical reactions or physical changes. It is used to determine the enthalpy changes of reactions.
Calorimetry: Calorimetry is the scientific process of measuring the heat energy released or absorbed during a chemical or physical process. It provides a way to quantify the energy changes that occur in a system, which is essential for understanding thermodynamic principles.
Coffee-Cup Calorimeter: A coffee-cup calorimeter is a simple device used to measure the heat energy released or absorbed during a chemical reaction or a physical change. It consists of a styrofoam or insulated cup that serves as a container for the reaction, allowing for the measurement of temperature changes and the calculation of the heat of the process.
Combustion reaction: A combustion reaction is a chemical process in which a substance (typically a hydrocarbon) reacts rapidly with oxygen to produce heat and light, resulting in the formation of products such as carbon dioxide and water. These reactions are essential for understanding energy transformations, particularly in calorimetry, where they can be used to measure the heat released during the process.
Constant-Pressure Calorimeter: A constant-pressure calorimeter is an instrument used in calorimetry to measure the heat of reaction or the heat capacity of a substance under conditions of constant pressure. It is a vital tool for understanding energy changes in chemical and physical processes.
Constant-Volume Calorimeter: A constant-volume calorimeter is a device used in calorimetry to measure the amount of heat released or absorbed during a chemical reaction or physical process. It maintains a constant volume throughout the experiment, allowing for the direct measurement of changes in temperature and the calculation of the associated enthalpy change.
Energy Conservation: Energy conservation is the concept that energy can neither be created nor destroyed, but rather transformed or transferred from one form to another. This fundamental principle, known as the first law of thermodynamics, is a cornerstone of scientific understanding and has far-reaching implications across various fields, including chemistry.
Enthalpy: Enthalpy is a measure of the total energy of a thermodynamic system, including both the internal energy of the system and the work done by or on the system due to changes in pressure and volume. It is a key concept in understanding the energy changes that occur during chemical reactions and phase changes.
Enthalpy (H): Enthalpy (H) is the total heat content of a system at constant pressure. It is a thermodynamic property that includes internal energy and the product of pressure and volume.
Exothermic: Exothermic refers to a chemical reaction or process that releases energy in the form of heat to the surrounding environment. These reactions produce more energy than they consume, resulting in a net release of heat.
Exothermic process: An exothermic process is a chemical reaction or physical change that releases heat to its surroundings. This release of energy usually results in an increase in the temperature of the surroundings.
First law of thermodynamics: The first law of thermodynamics states that energy cannot be created or destroyed, only transferred or converted from one form to another. In chemistry, it is often formulated as $\Delta U = Q - W$, where $\Delta U$ is the change in internal energy, $Q$ is the heat added to the system, and $W$ is the work done by the system.
First Law of Thermodynamics: The First Law of Thermodynamics states that energy can be converted from one form to another, but it cannot be created or destroyed. It is the principle of conservation of energy, which says that the total energy of an isolated system is constant and energy can neither be created nor destroyed, but can only be transformed or transferred from one form to another.
Heat Capacity: Heat capacity is a measure of the amount of energy required to raise the temperature of a substance by one degree. It is a fundamental property that describes how much heat a material can absorb or release without undergoing a phase change.
Heat capacity (C): Heat capacity (C) is the amount of heat energy required to raise the temperature of a substance by one degree Celsius. It is an extensive property dependent on the quantity of the substance.
Heat of Combustion: The heat of combustion is the amount of energy released or absorbed when a substance undergoes complete combustion, where a fuel is oxidized in the presence of oxygen to form carbon dioxide and water. It is a fundamental concept in calorimetry, the study of heat transfer in chemical reactions.
Heat of Solution: The heat of solution is the amount of heat released or absorbed when a solute is dissolved in a solvent to form a solution. It represents the enthalpy change that occurs during the dissolution process and is an important concept in the study of calorimetry.
Joule: The joule (J) is the standard unit of energy in the International System of Units (SI). It measures the amount of work done or energy transferred when a force of one newton acts upon an object to provide a displacement of one meter in the direction of the force.
Nutritional calorie (Calorie): A nutritional calorie (Calorie), denoted with a capital 'C', is the amount of energy needed to raise the temperature of 1 kilogram of water by 1 degree Celsius. It is equivalent to 1,000 small calories (cal).
Specific Heat Capacity: Specific heat capacity is a measure of the amount of energy required to raise the temperature of a substance by one degree. It quantifies a material's ability to store thermal energy and is an important property in understanding energy transfers and thermodynamic processes.
Specific heat capacity (c): Specific heat capacity ($c$) is the amount of heat required to raise the temperature of one gram of a substance by one degree Celsius. It is a property that varies between different materials.
Surroundings: Surroundings in thermochemistry refers to everything outside the system being studied. It includes all external factors that can exchange energy with the system.
System: A system is the part of the universe being studied, isolated for observation and measurement. In thermochemistry, it refers to the specific set of reactants and products involved in a reaction.
Thermal Equilibrium: Thermal equilibrium is a state in which a system and its surroundings have the same temperature, and there is no net transfer of thermal energy between them. This occurs when the system and its surroundings have reached a balance in their temperatures, and the flow of heat is zero.
Thermochemistry: Thermochemistry is the study of the heat energy involved in chemical reactions and changes of state. It focuses on how energy is absorbed or released during these processes.
Thermochemistry: Thermochemistry is the study of the energy changes that occur during chemical reactions and phase changes. It focuses on the relationship between chemical processes and the associated transfer of heat energy.