4.3 Reaction Stoichiometry
3 min read•june 24, 2024
Reaction is all about the numbers behind chemical reactions. It helps us figure out how much stuff we need to make things happen in the lab and in real life. This is super useful for everything from cooking to rocket science!
We'll learn how to balance equations, calculate amounts of and , and solve problems involving mass and concentration. These skills are key for understanding how chemicals interact and for making precise measurements in chemistry experiments.
Reaction Stoichiometry
Stoichiometry in chemical reactions
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- Quantitative study of and in a chemical reaction
- Calculates quantities of substances consumed or produced (, , )
- Helps determine limiting reactants and theoretical yields
- Based on the
- Total mass of reactants equals total mass of products
- Atoms are neither created nor destroyed, only rearranged
- Uses mole ratios derived from balanced chemical equations
- Compares relative amounts of reactants and products
- Coefficients in balanced equation represent mole ratios ( + → 2 )
Reactant and product quantity calculations
- Start with a
- Ensure equal number of atoms of each element on both sides (2 H₂ + → 2 )
- Determine between reactants and products
- Use coefficients in balanced equation to establish mole ratio (2:1:2 for H₂:O₂:H₂O)
- Convert given quantities (mass, volume, moles) of reactants or products to moles
- (g/mol) for solids and liquids (: 58.44 g/mol)
- (22.4 L/mol at ) for gases (O₂: 22.4 L/mol at STP)
- Use mole ratio to calculate moles of unknown reactant or product
- Apply mole ratio from balanced equation (2 mol H₂ : 1 mol O₂)
- Convert calculated moles back to desired unit (mass, volume, moles)
- for mass, molar volume for gases, for solutions
- Use to ensure correct unit conversions
Mass, mole, and concentration problems
- For solutions, use concentration (molarity, M) to convert between volume and moles
- = moles of solute / liters of solution (0.5 M NaCl = 0.5 mol NaCl / 1 L solution)
- Moles of solute = Molarity (M) × liters of solution (2.5 L of 0.5 M NaCl = 1.25 mol NaCl)
- When given mass of reactant or product, convert to moles using molar mass
- Moles = mass (g) / molar mass (g/mol) (5 g NaCl / 58.44 g/mol = 0.0856 mol NaCl)
- Apply mole ratio from balanced chemical equation to determine moles of unknown substance
- Use coefficients to set up proportion (2 mol H₂ : 1 mol O₂ = 4 mol H₂ : x mol O₂, solve for x)
- Convert calculated moles to desired unit (mass, volume, concentration)
- Mass (g) = moles × molar mass (g/mol) (0.0856 mol NaCl × 58.44 g/mol = 5 g NaCl)
- Volume (L) = moles × molar volume (22.4 L/mol at STP) for gases (1 mol O₂ × 22.4 L/mol = 22.4 L O₂ at STP)
- Volume (L) of solution = moles of solute / molarity (M) (0.5 mol NaCl / 0.5 M = 1 L NaCl solution)
Additional Stoichiometric Concepts
- : Compares actual yield to in a reaction
- : Reactant present in greater quantity than required by stoichiometry
- : Simplest whole-number ratio of atoms in a compound
- : When reactants are present in exact proportions according to balanced equation
Key Terms to Review (39)
Balanced Chemical Equation: A balanced chemical equation is a representation of a chemical reaction that accurately depicts the conservation of matter. It ensures that the number of atoms of each element is the same on both sides of the equation, indicating that no atoms are created or destroyed during the reaction.
Cl₂: Cl₂ is the chemical formula for chlorine gas, a diatomic molecule consisting of two chlorine atoms covalently bonded together. This term is important in the context of ionic and molecular compounds as well as reaction stoichiometry, as chlorine is a highly reactive element that forms various compounds and participates in numerous chemical reactions.
Dimensional analysis: Dimensional analysis is a mathematical technique used to convert one set of units to another. It involves multiplying by conversion factors that express the same quantity in different units.
Dimensional Analysis: Dimensional analysis is the process of analyzing and manipulating the dimensions of physical quantities to verify the dimensional consistency of equations, convert between different units, and solve problems involving multiple measurements. It is a powerful tool used in various scientific and engineering fields to ensure the validity and accuracy of calculations and relationships between physical quantities.
Empirical formula: An empirical formula represents the simplest whole-number ratio of elements in a compound. It does not show the actual number of atoms, but rather the relative proportions.
Empirical Formula: The empirical formula represents the simplest whole-number ratio of atoms of each element present in a compound. It provides the most basic representation of the composition of a compound without specifying the actual number of atoms present.
Excess reactant: An excess reactant is a substance that remains after a chemical reaction has reached completion. It is the reactant that is not entirely consumed in the reaction.
Excess Reactant: The excess reactant in a chemical reaction is the reactant that is present in a greater amount than is required to completely consume the other reactant(s). It remains in the reaction mixture after the limiting reactant has been fully consumed.
Grams: Grams are a unit of measurement in the metric system that is used to quantify the mass or weight of an object or substance. It is a fundamental unit in chemistry and plays a crucial role in various chemical concepts and calculations.
H₂: H₂ is the chemical formula representing a diatomic molecule composed of two hydrogen atoms. This term is particularly relevant in the context of Reaction Stoichiometry, as H₂ is a common reactant or product in various chemical reactions.
H₂O: H₂O, commonly known as water, is a chemical compound consisting of two hydrogen atoms and one oxygen atom. It is a vital substance that plays a crucial role in various chemical and biological processes, including those related to ionic and molecular compounds as well as reaction stoichiometry.
HCl: HCl, or hydrogen chloride, is a chemical compound consisting of one hydrogen atom and one chlorine atom. It is a colorless, corrosive gas that has a wide range of applications and plays a crucial role in various chemical processes and reactions.
Law of Conservation of Mass: The law of conservation of mass states that the total mass of the reactants in a chemical reaction is equal to the total mass of the products. This means that matter cannot be created or destroyed during a chemical process, but rather it is conserved and simply changes form.
Limiting reactant: The limiting reactant in a chemical reaction is the substance that is entirely consumed first, limiting the amount of products formed. It determines the maximum yield of the reaction.
Limiting Reactant: The limiting reactant is the reactant in a chemical reaction that is completely consumed, thereby determining the maximum amount of product that can be formed. It is the reactant that runs out first, limiting the overall reaction progress.
Liters: Liters (L) is a unit of measurement used to quantify the volume of a substance, particularly in the context of chemistry. It is a metric unit that is commonly used to measure the volume of liquids and gases.
Molar mass: Molar mass is the mass of one mole of a substance, expressed in grams per mole (g/mol). It is calculated by summing the atomic masses of all atoms in the molecular formula.
Molar Mass: Molar mass is the mass of one mole of a substance, expressed in grams per mole (g/mol). It is a fundamental concept in chemistry that relates the mass of a substance to the number of particles (atoms, molecules, or ions) it contains, and is essential for understanding chemical formulas, stoichiometry, and the behavior of gases.
Molar Volume: Molar volume is the volume occupied by one mole of a substance at a given temperature and pressure. It is a fundamental concept in chemistry that relates the amount of a substance to its physical volume and is essential for understanding the behavior of gases, reaction stoichiometry, and the ideal gas law.
Molarity: Molarity is a measure of the concentration of a solution, specifically the number of moles of a solute dissolved per liter of solution. It is a fundamental concept in chemistry that is used to quantify the amount of a substance present in a given volume of a solution and is essential for understanding various chemical processes and analyses.
Molarity (M): Molarity (M) is a measure of the concentration of a solute in a solution, expressed as moles of solute per liter of solution. It is commonly used to quantify the concentration of chemical solutions in laboratory settings.
Mole Ratio: The mole ratio is a fundamental concept in chemistry that describes the relationship between the quantities of reactants and products in a balanced chemical equation. It allows for the quantitative analysis of chemical reactions by providing a means to determine the amounts of substances involved based on the balanced stoichiometric coefficients.
Moles: A mole is a unit of measurement in chemistry that represents a fixed number of particles, such as atoms, molecules, or ions. It serves as a bridge between the microscopic world of chemical reactions and the macroscopic world of observable quantities.
NaCl: NaCl, commonly known as sodium chloride, is a chemical compound that consists of one sodium atom (Na) and one chlorine atom (Cl) bonded together. It is an ionic compound that is essential for various biological and industrial processes, and it is the primary component of table salt.
O₂: Oxygen (O₂) is a colorless, odorless, and highly reactive gas that is essential for life. It is the second most abundant element in the Earth's atmosphere and plays a crucial role in various chemical and biological processes, including respiration, combustion, and photosynthesis.
Orbital diagrams: Orbital diagrams are graphical representations of the electron configurations in atoms. They use boxes or lines to represent orbitals and arrows to represent electrons with their spins.
Percent yield: Percent yield is the ratio of the actual yield to the theoretical yield, expressed as a percentage. It measures the efficiency of a chemical reaction.
Percent Yield: Percent yield is a measure of the efficiency of a chemical reaction, representing the ratio of the actual amount of product obtained to the theoretical maximum amount of product that could be produced under ideal conditions.
Products: Products are the substances formed as a result of a chemical reaction. They appear on the right side of a balanced chemical equation.
Products: In the context of chemistry, products refer to the substances that are formed as the result of a chemical reaction. They are the final compounds or materials that emerge from the transformation of the reactants, the starting substances, through the breaking and forming of chemical bonds.
Reactants: Reactants are the starting substances in a chemical reaction that undergo change to form products. They are present on the left side of a chemical equation.
Reactants: Reactants are the starting substances in a chemical reaction that undergo transformation to produce new products. They are the initial materials that come together and interact to initiate a chemical change.
Standard molar volume: Standard molar volume is the volume occupied by one mole of an ideal gas at standard temperature and pressure (STP), which is 0°C (273.15 K) and 1 atm pressure. It is approximately 22.414 liters.
Stoichiometric factors: Stoichiometric factors are the coefficients in a balanced chemical equation that indicate the relative amounts of reactants and products involved. These factors are used to convert between moles of different substances in a reaction.
Stoichiometric Point: The stoichiometric point is the point in a chemical reaction where the reactants are present in the exact proportions required by the balanced chemical equation. At this point, one of the reactants is completely consumed, and the reaction is said to be at its stoichiometric endpoint.
Stoichiometry: Stoichiometry is the calculation of reactants and products in chemical reactions using balanced chemical equations. It involves the use of molar ratios derived from these equations to predict quantities of substances consumed and produced.
STP: STP stands for Standard Temperature and Pressure, which is a set of conditions often used as a reference point in chemistry for measuring gases. Specifically, STP is defined as a temperature of 0 degrees Celsius (273.15 K) and a pressure of 1 atmosphere (101.3 kPa). Understanding STP is essential in reaction stoichiometry because it allows for consistent comparisons of gas volumes and supports calculations involving the ideal gas law.
Theoretical yield: Theoretical yield is the maximum amount of product that can be produced in a chemical reaction based on the stoichiometric calculations from the balanced equation. It assumes perfect conditions with no losses or side reactions.
Theoretical Yield: Theoretical yield is the maximum amount of product that can be obtained from a chemical reaction based on the limiting reactant and the balanced chemical equation. It represents the ideal, stoichiometric amount of product that could be produced if the reaction proceeds to completion without any losses or side reactions.