Chemical equations are the language of chemistry, showing how substances change during reactions. Balancing these equations ensures we follow the law of conservation of mass, keeping track of all atoms involved.
In this section, we'll learn how to balance equations using different methods. We'll also explore the concept of limiting reactants and how balanced equations help us calculate product yields in chemical reactions.
Conservation of Mass in Chemical Equations
The Law of Conservation of Mass
- The law of conservation of mass states that matter is neither created nor destroyed in chemical reactions
- The total mass of the products must equal the total mass of the reactants
- This law is fundamental to balancing chemical equations and understanding the quantitative aspects of chemical reactions
Balanced Chemical Equations
- In a balanced chemical equation, the number of atoms of each element is equal on both the reactant and product sides of the equation
- The coefficients in a balanced chemical equation represent the relative number of moles of each substance involved in the reaction
- Subscripts in chemical formulas cannot be changed to balance an equation as they represent the actual number of atoms in a molecule (H2O, CO2)
Balancing Chemical Equations
Least Common Multiple (LCM) Method
- The LCM method involves finding the least common multiple of the number of atoms of each element on the reactant and product sides
- Divide the LCM by the actual number of atoms to obtain the coefficients
- This method is systematic and can be applied to complex equations with multiple elements and compounds
Inspection Method
- The inspection method involves trial and error, adjusting coefficients until the number of atoms of each element is equal on both sides of the equation
- Begin by balancing elements that appear in only one compound on each side of the equation (Na, Cl)
- Next, balance elements that appear in more than one compound on either side of the equation (C, O)
- Finally, balance hydrogen and oxygen atoms, adjusting the coefficient of H2O if necessary
- Fractional coefficients are not allowed in balanced equations. If obtained, multiply all coefficients by a common denominator to obtain whole numbers
Significance of Balanced Equations
Mole Ratios and Stoichiometry
- Balanced chemical equations provide information about the mole ratios of reactants and products in a reaction
- The coefficients can be used to determine the molar mass of reactants consumed and products formed
- Stoichiometry, the quantitative study of reactants and products, relies on balanced equations to calculate the amounts of substances involved
Theoretical Yield
- The mole ratios derived from balanced equations can be used to determine the theoretical yield of a product in a chemical reaction
- Theoretical yield is the maximum amount of product that can be formed based on the balanced equation and the limiting reactant
- Actual yield is often less than theoretical yield due to factors like incomplete reactions, side reactions, and losses during purification
Limiting vs Excess Reactants
Identifying the Limiting Reactant
- The limiting reactant is the reactant that is completely consumed in a chemical reaction and limits the amount of product that can be formed
- The excess reactant is the reactant that remains after the limiting reactant has been completely consumed
- To determine the limiting reactant, calculate the molar amounts of each reactant and compare them to the mole ratios in the balanced equation
Calculating Product Formation
- Divide the actual molar amount of each reactant by its coefficient in the balanced equation to find the molar amount of product that could be formed by each reactant
- The reactant that yields the least amount of product is the limiting reactant
- The amount of product formed in a reaction is determined by the amount of the limiting reactant and the mole ratios in the balanced equation
- Excess reactants do not contribute to additional product formation once the limiting reactant is depleted