Q: Which of the following equations correctly expresses percent yield?

$$\text{Percent yield} = \dfrac{\text{actual yield}}{\text{theoretical yield}} \times 100\%$$

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: $$2\ \mathrm{C_8H_{18}}(l) + 25\ \mathrm{O_2$}(g) \rightarrow 16\ \mathrm{CO_2$}(g) + 18\ \mathrm{H_2O}(g)$$, how many moles of $$\mathrm{CO_2$}$$ are produced from 5 moles of $$\mathrm{C_8H_{18}}$$?

Accepted Answer

$$40$$ moles

Question 3

A car burns $$5.0 	imes 10^2$ g of octane ($$\mathrm{C_8H_{18}}$$). Using the molar mass of octane (114.3$ g/mol) and 44.01$ g/mol for $$\mathrm{$$CO_2$$}$$, how many grams of $$\mathrm{$$CO_2$$}$$ are produced? (Balanced equation: 2$$\ \mathrm{C_8H_{18}} + 25\ \mathrm{$$O_2$$} ightarrow 16\ \mathrm{$$CO_2$$} + 18\ \mathrm{H_2O}$$)

Accepted Answer

$$1.5 	imes 10^3$ g

Question 4

Which of the following statements about limiting reactants is correct?

Accepted Answer

The limiting reactant is completely consumed in the reaction and determines the theoretical yield.

Question 5

In the reaction $$2\ \mathrm{Na}(s) + \mathrm{Cl_2$}(g) \rightarrow 2\ \mathrm{NaCl}(s)$$, if you start with $$53.2 g Na $$and $$65.8 g$$ $$\mathrm{Cl_2$}$$, what is the theoretical yield of $$\mathrm{NaCl} in $$grams? (Molar masses: Na = $$22.99 g/$$mol, $$\mathrm{Cl_2$}$$ = $$70.90 g/$$mol, $$\mathrm{NaCl}$$ = $$58.44 g/$$mol)

Accepted Answer

$$108 g$$

Question 6

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

Accepted Answer

$$85.9\%$$

Question 7

Which of the following equations correctly expresses percent yield?

Accepted Answer

$$	ext{Percent yield} = \dfrac{	ext{actual yield}}{	ext{theoretical yield}} 	imes 100\%$$

Question 8

Which of the following best describes an exothermic reaction?

Accepted Answer

A reaction that releases heat to the surroundings and has a negative $$\Delta H_{\mathrm{rxn}}.$$

Question 9

The combustion of methane is represented by: $$\mathrm{CH_4$}(g) + 2\ \mathrm{O_2$}(g) \rightarrow \mathrm{CO_2$}(g) + 2\ \mathrm{H_2O}(g)$$, $$\Delta H_{\mathrm{rxn}} = -802.3 kJ. $$What does the negative sign indicate?

Accepted Answer

The reaction is exothermic and releases heat.

Question 10

How much heat (in kJ) is released when $$1.18 	imes 10^4$ g of propane ($$\mathrm{C_3H_8}$$, molar mass 44.11$ g/mol) is completely combusted? ($$\Delta H_{\mathrm{rxn}} = -2044$$ kJ per mol $$\mathrm{C_3H_8}$$)

Accepted Answer

$$5.47 	imes 10^5$ kJ

Question 11

Which of the following is NOT a correct step in a mass-to-mass stoichiometry calculation?

Accepted Answer

Add the masses of all reactants to get the mass of product.

Question 12

A Bunsen burner flame is adjusted to have a sharp, inner blue triangle and no smoke. What does this indicate about the air (oxygen) supply?

Accepted Answer

The air supply is at its optimum, resulting in complete combustion.

Question 13

In the reaction $$\mathrm{N_2$}(g) + 3\ \mathrm{H_2$}(g) \rightarrow 2\ \mathrm{NH_3$}(g)$$, how many moles of $$\mathrm{NH_3$}$$ can be produced from $$3$$ mol of $$\mathrm{N_2$}$$ and excess $$\mathrm{H_2$}$$?

Accepted Answer

$$6$$ mol

Question 14

Which of the following is true about the theoretical yield in a chemical reaction?

Accepted Answer

It is the maximum amount of product that can be formed from the limiting reactant.

Question 15

A reaction between $$1.8$$ mol Ti and $$3.2$$ mol $$\mathrm{Cl_2$}$$ produces $$\mathrm{$$TiCl_4$$}$$ according to $$\mathrm{Ti} + 2\ \mathrm{Cl_2$} \rightarrow \mathrm{$$TiCl_4$$}. $$What is the limiting reactant and the theoretical yield (in mol) of $$\mathrm{$$TiCl_4$$}$$?

Accepted Answer

Limiting reactant: $$\mathrm{Cl_2$}$$; Theoretical yield: $$1.6$$ mol

Question 16

Which of the following best describes an endothermic reaction?

Accepted Answer

A reaction that absorbs heat from the surroundings and has a positive $$\Delta H_{\mathrm{rxn}}.$$

Question 17

Which of the following is a correct conversion factor for the reaction $$2\ \mathrm{Na}(s) + \mathrm{Cl_2$}(g) \rightarrow 2\ \mathrm{NaCl}(s)$$?

Accepted Answer

$$\dfrac{2\ \mathrm{mol\ NaCl}}{2\ \mathrm{mol\ Na}}$$

Chapter 8: Quantities in Chemical Reactions – Study Guide

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