Aim: Using mole ratios in balanced chemical equations

What is Stoichiometry? Stoichiometry is the part of chemistry that studies amounts of substances that are involved in reactions.

Using Balanced Chemical Equations The coefficients in a balanced chemical equations shows a relationship between the reactants and the products. Chemists use a balanced chemical equation to calculate how much reactant is needed or a product is formed in a reaction.

Using Balanced Chemical Equation

•A balanced chemical equation can tell us:•The ratio of the number of molecules of each type reacting.•The ratio of the moles of each reactant and product.•The ratio of the moles of each reactant and product in a reaction is known as the mole ratio.•The mole ratio can be used to calculate the number of moles and mass of reactants and products.

Mole Ratio The mole ratio is the ratio of reactants and products and is the ratio of the coefficients for reactants and products found in the balanced chemical reaction.

In the reaction 2Mg(s) + O2(g) 2MgO(s) , the ratio of Mg : O2 : MgO is 2 : 1 : 2.

Example Given the formula

◦ 2Mg(s) + O2(g) 2MgO(s)How many moles of magnesium are needed to react with 3.7 O2?

Set up ratio:

= Solve for x x= (3.7 x 2)/1

X= 7.4 mol Mg

Example 2 How many moles pf ammonia are produced when 0.60 mol of nitrogen reacts with hydrogen? Step 1: Write balanced chemical equation Step 2: Set up ratio Step 3: solve for x

You try! 1. How many moles of calcium are needed to react completely with 6 moles of H2O in the following reaction:◦Ca + 2H2O Ca(OH)2 + H2

2. Given the reaction:◦CH4(g) + 2 O2 (g) CO2(g) + 2H2O(g)

How many moles of oxygen are needed for the complete combustion of 3.0 moles of CH4(g)?