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Understanding Balanced Chemical Equations and Mole Ratios

Learn how balanced equations show proportions, express amounts in moles, and define mole ratios in chemistry. Practice questions included.

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Understanding Balanced Chemical Equations and Mole Ratios

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  1. Balanced Equations Show Proportions A balanced chemical equation is very similar to a recipe in that the coefficients in the balanced equation show the proportions of the reactants and products involved in the reaction. On a very small scale, the coefficients in a balanced equation represent the numbers of particles for each substance in the reaction. For example: 2H2 + O2 → 2H2O The balance equation above states that 2 hydrogen molecules are reacting with 1 oxygen molecule to produce 2 water molecules.

  2. Relative Amounts in Equations Can Be Expressed in Moles Just as you can interpret equations in terms of particles, you can interpret them in terms of moles. The coefficients in a balanced equation also represent the moles of each substance. For example: 2H2 + O2 → 2H2O The balance equation above states that 2 moles of hydrogen molecules are reacting with 1 mole of oxygen molecule to produce 2 moles of water molecules.

  3. The Mole Ratio The coefficients in a balanced chemical equation show the relative numbers of moles of the substances in the reaction. As a result, you can use the coefficients in conversion factors called mole ratios. Mole ratios bridge the gap and can convert from moles of one substance to moles of another. For example: 2H2 + O2 → 2H2O In the equation above the mole ration between oxygen and water is1:2 This means that for every mole of oxygen used 2 moles of water are produced It also means that for every mole of water produced only 0.5 moles of oxygen are used.

  4. Practice Make Perfect 1. Given the balanced equation representing a reaction: F2(g) + H2(g)  2HF(g) What is the mole ratio of H2(g) to HF(g) in this reaction? 1:2 2. Given the reaction: PbCl2(aq) + Na2CrO4(aq)  PbCrO4(s) + 2NaCl(aq) What is the total number of moles of NaCl formed when 2 moles of Na2CrO4 react completely? 4 moles of NaCl

  5. 3. Given the balanced equation: 2C4H10(g) + 13O2(g)  8CO2(g) + 10H2O(g) What is the total number of moles of O2(g) that must react completely with 5.00 moles of C4H10(g)? 32.5 moles of O2 4. Given the balanced equation: 2C + 3H2 C2H6 What is the total number of moles of C that must completely react to produce 2.0 moles of C2H6? 4 moles of Carbon 5. Given the equation: 2C2H2(g) + 5O2(g)  4CO2(g) + 2H2O(g) How many moles of oxygen are required to react completely with 1.0 mole of C2H2? 2.5 moles of O2

  6. 6. Given the reaction: N2(g) + 3H2(g)  2NH3(g) What is the mole-to-mole ratio between nitrogen gas and hydrogen gas? 1:3 7. Given the reaction: 6CO2 + 6H2O  C6H12O6 + 6O2 What is the total number of moles of water needed to make 2.5 moles of C6H12O6? 15 moles of water

  7. Questions 8 and 9 refer to the following: Given the reaction: 2C2H6 + 7O2 4CO2 + 6H2O 8) What is the ratio of moles of CO2 produced to moles of C2H6 consumed? 9) What is the total number of moles of CO2 produced by the complete combustion of 5.0 moles of C2H6? 4:2  2:1 10 moles of CO2

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