Science: Stoichiometry Calculations
Using balanced equations to calculate amounts of reactants and products
Science: Stoichiometry Calculations
Using balanced equations to calculate amounts of reactants and products
Science - Grade 9-12
- 1
Hydrogen gas reacts with oxygen gas to form water: 2H2 + O2 -> 2H2O. If 4.0 moles of H2 react completely, how many moles of H2O are produced?
Use the coefficients in the balanced equation as a mole ratio.
4.0 moles of H2O are produced because the mole ratio of H2 to H2O is 2 to 2, which simplifies to 1 to 1. - 2
Using the equation N2 + 3H2 -> 2NH3, how many moles of NH3 can be produced from 5.0 moles of H2 if nitrogen is in excess?
3.3 moles of NH3 can be produced. Using the ratio 3 moles H2 to 2 moles NH3, 5.0 x 2/3 = 3.3 moles NH3. - 3
Calcium carbonate decomposes according to the equation CaCO3 -> CaO + CO2. If 2.50 moles of CaCO3 decompose completely, how many moles of CO2 are formed?
Look for a 1 to 1 relationship in the equation.
2.50 moles of CO2 are formed because the ratio of CaCO3 to CO2 is 1 to 1 in the balanced equation. - 4
Methane burns in oxygen according to the equation CH4 + 2O2 -> CO2 + 2H2O. If 16.0 grams of CH4 react completely, how many grams of CO2 are produced?
Convert grams to moles first using molar mass.
44.0 grams of CO2 are produced. First, 16.0 grams of CH4 is 1.00 mole of CH4. The mole ratio from CH4 to CO2 is 1 to 1, so 1.00 mole of CO2 forms, which has a mass of 44.0 grams. - 5
For the reaction 2Na + Cl2 -> 2NaCl, how many grams of NaCl are produced when 4.60 moles of Na react completely with excess chlorine gas?
269 grams of NaCl are produced. The mole ratio of Na to NaCl is 1 to 1, so 4.60 moles of Na form 4.60 moles of NaCl. Multiplying by the molar mass of NaCl, about 58.44 grams per mole, gives about 269 grams. - 6
Using the equation 2Al + 3Cl2 -> 2AlCl3, how many moles of Cl2 are required to react completely with 6.0 moles of Al?
Set up a conversion factor from aluminum to chlorine gas.
9.0 moles of Cl2 are required. The mole ratio is 2 moles of Al to 3 moles of Cl2, so 6.0 x 3/2 = 9.0 moles of Cl2. - 7
Iron reacts with sulfur to form iron(II) sulfide: Fe + S -> FeS. If 11.2 grams of Fe react completely, how many grams of FeS are produced?
17.6 grams of FeS are produced. First, 11.2 grams of Fe is about 0.200 moles of Fe. The ratio from Fe to FeS is 1 to 1, so 0.200 moles of FeS form. Multiplying by the molar mass of FeS, about 87.9 grams per mole, gives about 17.6 grams. - 8
Balance the equation for the formation of aluminum oxide and then answer the question: Al + O2 -> Al2O3. If 8.0 moles of O2 react completely, how many moles of Al2O3 are produced?
Balance the equation before using any mole ratios.
The balanced equation is 4Al + 3O2 -> 2Al2O3. From the ratio 3 moles of O2 to 2 moles of Al2O3, 8.0 x 2/3 = 5.3 moles of Al2O3 are produced. - 9
Propane combusts according to the equation C3H8 + 5O2 -> 3CO2 + 4H2O. If 2.0 moles of C3H8 burn completely, how many moles of H2O are formed?
8.0 moles of H2O are formed. The mole ratio from C3H8 to H2O is 1 to 4, so 2.0 x 4 = 8.0 moles of H2O. - 10
Using the equation 2KClO3 -> 2KCl + 3O2, how many grams of O2 are produced from the complete decomposition of 24.5 grams of KClO3?
Convert KClO3 from grams to moles, then use the mole ratio, then convert to grams of O2.
9.6 grams of O2 are produced. First, 24.5 grams of KClO3 is about 0.200 moles of KClO3. Using the ratio 2 moles of KClO3 to 3 moles of O2 gives 0.300 moles of O2. Multiplying by 32.00 grams per mole gives 9.6 grams of O2. - 11
Zinc reacts with hydrochloric acid according to the equation Zn + 2HCl -> ZnCl2 + H2. If 13.1 grams of Zn react completely, how many grams of H2 are produced?
0.404 grams of H2 are produced. First, 13.1 grams of Zn is about 0.200 moles of Zn. The ratio from Zn to H2 is 1 to 1, so 0.200 moles of H2 form. Multiplying by the molar mass of H2, about 2.02 grams per mole, gives about 0.404 grams. - 12
Nitrogen monoxide reacts with oxygen to form nitrogen dioxide: 2NO + O2 -> 2NO2. If 7.5 moles of NO react completely, how many moles of O2 are needed?
Use the coefficient ratio between NO and O2.
3.75 moles of O2 are needed. The balanced equation shows that 2 moles of NO react with 1 mole of O2, so 7.5 x 1/2 = 3.75 moles of O2. - 13
Silver nitrate reacts with sodium chloride according to the equation AgNO3 + NaCl -> AgCl + NaNO3. If 1.70 moles of AgNO3 react completely, how many moles of AgCl form?
1.70 moles of AgCl form because the balanced equation shows a 1 to 1 mole ratio between AgNO3 and AgCl. - 14
Consider the reaction 2Mg + O2 -> 2MgO. If 12.0 grams of Mg react with 10.0 grams of O2, identify the limiting reactant and determine how many grams of MgO can form.
Convert both reactants to moles and compare the amount needed by the balanced equation.
Magnesium is the limiting reactant, and 19.9 grams of MgO can form. Twelve point zero grams of Mg is about 0.494 moles, while 10.0 grams of O2 is about 0.313 moles. The reaction needs 1 mole of O2 for every 2 moles of Mg, so 0.494 moles of Mg need only 0.247 moles of O2. Because there is more than enough oxygen, Mg limits the reaction. The mole ratio from Mg to MgO is 1 to 1, so 0.494 moles of MgO form, which is about 19.9 grams. - 15
Hydrogen gas reacts with chlorine gas according to the equation H2 + Cl2 -> 2HCl. If 3.0 moles of H2 and 4.0 moles of Cl2 are available, determine the limiting reactant and calculate how many moles of HCl can be produced.
Hydrogen is the limiting reactant, and 6.0 moles of HCl can be produced. The equation requires a 1 to 1 ratio of H2 to Cl2. Since only 3.0 moles of H2 are available, only 3.0 moles of Cl2 can react even though 4.0 moles are present. The ratio from H2 to HCl is 1 to 2, so 3.0 moles of H2 produce 6.0 moles of HCl.