University:
High School
Course:
High School Chemistry
Academic year:

2020
Views:

182

Pages:

7
Author:

tevredeneme

MATH CALCULATIONS INVOLVING EQUATIONS A chemical reaction in which reactants are changed to form products, can be written in equation form as follows: 2C₂H₆ + 7O₂ → 4CO₂ + 6H₂O The numbers in front of the formulas are COEFFICIENTS, they represent the number of MOLES of that substance. When working with chemical equations it is assumed that: The reaction is a SINGLE reaction (no side reactions). The reaction goes to COMPLETION (ONLY PRODUCTS REMAIN) The reactants are completely used. Use the COEFFICIENTS in front of the formula to get a mole ratio. 2C₂H₆ + 7O₂ → 4CO₂ + 6H₂O mole ratio: 2 : 7 : 4 : 6 This means that 2 moles of C₂H₆ combine with 7 moles of O₂ to produce 4 moles of CO₂ and 6 moles of water. Example: How many moles of water will be produced from the complete combustion of 3 moles of ethane (C₂H₆)? 2C₂H₆ + 7O₂ → 4CO₂ + 6H₂O Underline Compounds given in the problem + equation Step 1: Determine the mole ratio (MR) of ONLY those compounds asked about in the question. Mole Ratio (MR) → 2 mol C₂H₆ : 6 mol H₂O Step 2: Set up a proportion to solve for the unknown. Mole Ratio (MR) → 2 mol C₂H₆ = 6 mol H₂O info From Ques: → 3 mol C₂H₆ = X mol H₂O (Need Number, 20nd) 2X = 18 X = 9 mol H₂O SOLVING PROBLEMS USING EQUATIONS There are several types of equation problems. The following notes include a brief description of each and an example of how to solve the problem. MOLE - MOLE PROBLEMS These equation problems require that you give an answer in moles. LOOK FOR: A mole amount given in the problem and a question asking "how many moles..." Example 1: Given the reaction below, how many moles of ammonia are produced when 2 moles of nitrogen is consumed? N₂ (g) + 3H₂ (g) → 2NH₃ (g) Mole Ratio (MR) → 1 mol N₂ = 2 mol NH₃ Ques → 2 mol N₂ = X mol NH₃ X = 4 mol NH₃ Example 2: Given the balanced equation: 2Al + 3FeO → Al₂O₃ + 3Fe How many moles of Iron are produced when 4 moles of Aluminum is consumed? MR → 2 mol Al = 3 mol Fe Ques → 4 mol Al = X mol Fe X = 6 mol Fe VOLUME-VOLUME (liters-liters) PROBLEMS These problems require you to determine the number of liters produced from a given amount of liters used up. Moles + Liters can go in proportion together REMEMBER: 1 mole = 22.4 liters 2 moles = 44.8 L 3 moles = 67.2 L Example 1: How many liters of ethane (C₂H₆) can be completely oxidized by a reaction with 63 liters of oxygen? 2C₂H₆ (g) + 7O₂ (g) → 4CO₂ (g) + 6H₂O (g) MR → 2 mol C₂H₆ = 7 mol O₂ Ques → X L = 63 L O₂ 7X = 63 x 2 X = 18 L C₂H₆