Chapter 10 Stoichiometry Chapter Practice

Why must a chemical equation be balanced before you can determine mole ratios?

• Because the coefficients in a balanced equation directly represent the mole ratios of the reactants and products.

• Because balancing ensures that the charges are balanced in the equation.

• Because balancing eliminates any excess reactants.

• Because balancing influences the energy changes in a reaction.

Determine the relationships from a balanced chemical equation.

• Mole ratios among reactants and products

• The identity of the compounds only

• The rate of the reaction

• The equilibrium constant

Mole ratios are central to stoichiometric calculations because they provide conversion factors from one substance to another.

• They provide conversion factors from one substance to another.

• They ensure reaction conditions are optimal.

• They indicate reaction speed differences.

• They determine catalyst effects.

Determine the mole ratio that can convert moles of A to moles of B.

• 1:1

• 2:1

• 1:2

• Depends on reaction formula

Coefficients are used in mole ratios instead of subscripts because they indicate the relative number of molecules or moles involved in a reaction, while subscripts represent the fixed composition of a compound.

• They indicate the relative number of molecules or moles involved in a reaction

• They represent the fixed atomic composition of a molecule

• They can be changed arbitrarily to balance equations

• They denote the number of atoms in a molecule and are immutable

Balanced Chemical Equation: Explain how conservation of mass allows you to interpret a balanced chemical equation in terms of mass.

• It shows that the total mass of reactants equals the total mass of products.

• It proves that mass is created in a reaction.

• It indicates that mass is irrelevant in chemical equations.

• It suggests that the mass of reactants is less than the mass of products.

Write the mole ratios for this reaction that relate ammonium chromate to the products.

• 1 mole of ammonium dichromate decomposes to produce 1 mole of nitrogen gas, 1 mole of chromium(III) oxide, and 4 moles of water vapor.

• 1 mole of ammonium chromate produces 1 mole of nitrogen gas, 2 moles of chromium(III) oxide, and 3 moles of water vapor.

• 1 mole of ammonium chromate gives 2 moles of nitrogen gas, 1 mole of chromium(III) oxide, and 4 moles of water vapor.

• 1 mole of ammonium chromate yields 1 mole of nitrogen gas, 1 mole of chromium(III) oxide, and 2 moles of water vapor.

• The coefficients indicate the number of moles of each substance, which in turn represent the number of particles (when multiplied by Avogadro's number) and determine the mass (via molar mass).

• The coefficients indicate only the number of particles and have no relation to moles or mass.

• The equation shows that only mass is conserved, with no connection to moles or individual particles.

• The coefficients are arbitrary numbers with no chemical significance.

• The reactants break up into individual atoms and reform into products, with conservation of moles and mass despite a change in the number and types of particles.

• The reactants lose their molecular structure and become ions without any change in moles or mass.

• Only the mass is conserved while moles and number of particles are substantially changed.

• The reactants are converted into products without any rearrangement of atoms.

When solid copper is added to nitric acid, copper(II) nitrate, nitrogen dioxide, and water are produced. Which of the following shows the balanced chemical equation for the reaction along with six mole ratios?

• Cu + 4HNO3 → Cu(NO3)2 + 2NO2 + 2H2O; Mole ratios: Cu:HNO3 = 1:4, Cu:Cu(NO3)2 = 1:1, Cu:NO2 = 1:2, Cu:H2O = 1:2, HNO3:NO2 = 4:2, HNO3:H2O = 4:2.

• 3Cu + 8HNO3 → 3Cu(NO3)2 + 4NO + 4H2O; Mole ratios: Cu:HNO3 = 3:8, Cu:Cu(NO3)2 = 1:1, Cu:NO = 3:4, Cu:H2O = 3:4, HNO3:NO = 8:4, HNO3:H2O = 8:4.

• Cu + 2HNO3 → Cu(NO3)2 + NO2 + H2O; Mole ratios: Cu:HNO3 = 1:2, Cu:Cu(NO3)2 = 1:1, Cu:NO2 = 1:1, Cu:H2O = 1:1, HNO3:NO2 = 2:1, HNO3:H2O = 2:1.

• 2Cu + 6HNO3 → 2Cu(NO3)2 + 3NO2 + 3H2O; Mole ratios: Cu:HNO3 = 2:6, Cu:Cu(NO3)2 = 1:1, Cu:NO2 = 2:3, Cu:H2O = 2:3, HNO3:NO2 = 6:3, HNO3:H2O = 6:3.