Q: A reaction has a theoretical yield of 108 g NaCl, but only 86.4 g NaCl is actually produced. What is the percent yield?

$$\displaystyle \frac{86.4}{108} \times 100\% = 80\%$$

Q: Which of the following is the correct formula for calculating percent yield?

$$\displaystyle \frac{\text{actual yield}}{\text{theoretical yield}} \times 100\%$$

Q: A chemical reaction has a theoretical yield of 101.7 g Cu, but only 87.4 g Cu is obtained. What is the percent yield?

$$\displaystyle \frac{87.4}{101.7} \times 100\% = 86\%$$

Question 1

Which of the following best describes the greenhouse effect as it relates to global warming?

Accepted Answer

Greenhouse gases allow sunlight to enter the atmosphere but prevent heat from escaping, causing Earth's temperature to rise.

Question 2

Given the balanced equation for the combustion of octane: $$2\ \mathrm{C_8H_{18}} + 25\ \mathrm{O_2$} \rightarrow 16\ \mathrm{CO_2$} + 18\ \mathrm{H_2O}$$, how many moles of $$\mathrm{CO_2$}$$ are produced from 5 moles of octane, assuming excess oxygen?

Accepted Answer

$$40\ \mathrm{mol\ CO_2$}$$

Question 3

A recipe for pancakes requires 2 eggs for every 5 pancakes. If you have 12 eggs and enough of all other ingredients, how many pancakes can you make?

Accepted Answer

30 pancakes

Question 4

Which of the following is the correct definition of the limiting reactant in a chemical reaction?

Accepted Answer

The reactant that is completely consumed first, limiting the amount of product formed.

Question 5

If you start with 1.8 mol Ti and 3.2 mol Cl$$_2 in $$the reaction $$\mathrm{Ti} + 2\ \mathrm{Cl_2$} \rightarrow \mathrm{$$TiCl_4$$}$$, what is the theoretical yield of TiCl$$_4 in $$moles?

Accepted Answer

1.6 mol

Question 6

A reaction has a theoretical yield of 108 g NaCl, but only 86.4 g NaCl is actually produced. What is the percent yield?

Accepted Answer

$$\displaystyle \frac{86.4}{108} 	imes 100\% = 80\%$$

Question 7

Which of the following statements about exothermic and endothermic reactions is correct?

Accepted Answer

Exothermic reactions release heat to the surroundings and have a negative $$\Delta H_{rxn}.$$

Question 8

The combustion of propane ($$\mathrm{C_3H_8}) is $$represented by the equation: $$\mathrm{C_3H_8} + 5\ \mathrm{O_2$} \rightarrow 3\ \mathrm{CO_2$} + 4\ \mathrm{H_2O}$$, $$\Delta H_{rxn} = -2044\ \mathrm{kJ}. $$How much heat is released when 88.2 g of propane is burned completely?

Accepted Answer

$$-4088\ \mathrm{kJ}$$

Question 9

Which of the following best describes the relationship between reactants and products in a balanced chemical equation?

Accepted Answer

The equation shows the numerical (stoichiometric) relationship between reactants and products.

Question 10

A Bunsen burner flame is yellow and smoky. What adjustment should be made to achieve a hotter, blue flame?

Accepted Answer

Increase the amount of air entering the burner.

Question 11

Which of the following is the correct formula for calculating percent yield?

Accepted Answer

$$\displaystyle \frac{	ext{actual yield}}{	ext{theoretical yield}} 	imes 100\%$$

Question 12

If a reaction absorbs 182.6 kJ of heat when 1 mol N$$_2$$ reacts with 1 mol O$$_2 to $$form 2 mol NO, what is the sign of $$\Delta H_{rxn}$$ and what type of reaction is this?

Accepted Answer

$$\Delta H_{rxn} is $$positive; endothermic

Question 13

Which of the following is NOT a step in solving a mass-to-mass stoichiometry problem?

Accepted Answer

Multiply the mass of reactant by the mass of product.

Question 14

A chemical reaction has a theoretical yield of 101.7 g Cu, but only 87.4 g Cu is obtained. What is the percent yield?

Accepted Answer

$$\displaystyle \frac{87.4}{101.7} 	imes 100\% = 86\%$$

Question 15

Which of the following best explains why the actual yield of a chemical reaction is usually less than the theoretical yield?

Accepted Answer

Some product is lost or does not form due to side reactions or incomplete reactions.

Question 16

Which of the following is a correct statement about reaction stoichiometry?

Accepted Answer

It allows us to predict the amounts of products formed from given amounts of reactants.

Question 17

In the context of global warming, why is the combustion of fossil fuels a concern?

Accepted Answer

It produces carbon dioxide, a greenhouse gas that contributes to rising global temperatures.

Question 18

If you have 53.2 g Na and 65.8 g Cl$$_2$$ reacting to form NaCl, which reactant is limiting? (Molar masses: Na = 22.99 g/mol, Cl$$_2 = 70.90 g/$$mol)

Accepted Answer

Na

Chapter 8: Quantities in Chemical Reactions – Mini-Study Guide

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