Chemistry: SCI 1100
Stoichiometry
Objectives
Student will calculate mole ratios from a balanced chemical equation
Student will perform mole to mole stoichiometric calculations. Vocabulary mole ratio stoichiometry A conversion that expresses the relationship between any two substances in a chemical reaction in moles.
The calculation of the quantity of substances in a chemical reaction using the balanced equation. Compounds always have a set ratio. Water is always two part hydrogens to one part oxygen. Those ratios are very useful. In today’s lesson, we are going to start by examining a chemical equation. The ratios in this equation are as follows:
1 molecule of C H : 3 molecules of O : 2 molecules of CO : 2 molecules of H O
2 4 2 2 2 We need to think of this as a mole ratio.
1 mole of C H : 3 moles of O : 2 moles of CO : 2 moles of H O
2 4 2 2 2 Find the mass of each of the reactants or products
28.0 g/mol: 96.0 g/mol: 88.0 g/mol: 36.0
124 g/mol = 124g/mol The reactant side MUST equal the product side because of the Law of Conservation of Mass. How to Solve Stoichiometry Problems
Convert from grams to moles 1.
2. Use the molar ratio to determine the moles of the substances
Convert from moles to grams using the molar mass. 3. Let’s look at another example
There are 5.65 moles of F , how many moles of N and NF are there?
2 3 2 For the F multiply by the ratio of F to N arranged so the F will cancel out.
2, 2 2 2 For the NF , multiply by the ratio of F to NF arranged so the F will cancel out.
3 2 3 2 Both of these could be converted to grams easily enough.
Example 2 The following reaction produces 0.65 moles of CO . How much C H and O does it require as well as how much water does it need in grams?
2 Things we know. 2 4 2 0.65 moles CO 2 We can us the moles of CO and find the required moles of C H . We are again using the mole ratios.
2 2 It needs to be converted to grams. Use the same moles of CO , but a different ratio to find the moles of oxygen. 2 Then convert to grams
. Now for the water; using the same .65 mol CO 2 4 Then convert to grams Question 1 A certain reaction produced 14.80 mol carbon dioxide. How many moles of both Fe 2O3 and CO reacted? 44.40 mol Fe2O3; 133.2 mol CO
14.80 Fe2O3 ; 4.933 mol CO
9.867 mol Fe2O3 14.80 mol CO
4.933 mol Fe2O3 ; 14.80 mol Co Question 2
The coefficient of a particular substance in a balanced equation represents A. molecules (or formula units) B. moles, molecules and formula units C. moles D. mass Question 3
For the following equations, which is NOT a valid mole ratio? Question 4
Fluorine gas reacts with a solution of sodium bromide in a single­replacement producing aqueous sodium fluoride and bromine gas.
If a reaction starts with 0.480 mol fluorine gas, how many moles of sodium fluoride are produced? A. 0.960 mol B. 0.240 mol C. 1.92 mol D. 0.480 mol Question 5 In a certain reaction, 5.0 moles of hydrogen is reacted with excess nitrogen. To determine how many moles of ammonia are produced, what conversion factor should be used. (choose all that apply) Question 6
How many moles of ammonia are produced when 5 moles of hydrogen reacts with excess nitrogen? 3.3 mol 2.0 mol
10.0 mol
7.5 mol Question 7
Fluorine gas reacts with a solution of sodium bromide in a single­replacement producing aqueous sodium fluoride and bromine gas.
Which of the following is the correct balanced equation for this reaction? F2(g) + 2 NaBr (aq) ­­>2NaF (aq) + Br2(g)
2F(g) + NaBr2(aq) ­­>NaF2(aq) + 2 Br(g)
F(g) + NaBr(aq) ­­> NaF(aq) + Br(g)
F2(g) + NaBr(aq) ­­> NaF(aq) + Br2 (g) Question 8
How many moles of Fe2O3 are necessary to produce 0.824 mol of CO2? 0.549 mol 2.47 mol
0.275 mol
0.824 mol Question 9 How many moles of CO are required to completely react with 2.45 moles of Fe 2O3? 4.90 mol
2.45 mol
1.63 mol
7.35 mol Question 10
Which of the following are conserved in a chemical reaction? 1. number of atoms 2. mass 3. number of atoms and mass 4. number of moles and molecules 5. number of molecules 6. number of moles 7. All are correct

 

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