Question 1

Which of the following best describes the greenhouse effect as it relates to carbon dioxide?

Accepted Answer

CO2 allows visible light to enter the atmosphere but prevents heat energy from escaping.

Question 2

Given the balanced equation for the combustion of octane: $$2\ C_8H_{18}(l) + 25\ O_2$(g) \rightarrow 16\ CO_2$(g) + 18\ H_2O(g)$$, how many moles of $$CO_2$$ are produced from 4 moles of octane?

Accepted Answer

$$32\ mol$$

Question 3

If 5.0 $$	imes$$ $$10^2 g of $$pure octane ($$C_8H_{18}) is $$burned completely, what mass of $$CO_2 is $$emitted? (Molar mass of $$C_8H_{18} = 114.22 g/$$mol, $$CO_2 = 44.01 g/$$mol)

Accepted Answer

$$1540\ g$$

Question 4

Which statement about limiting reactants is correct?

Accepted Answer

The limiting reactant is the one that determines the maximum amount of product formed.

Question 5

A reaction yields 73% of the theoretical yield. If the theoretical yield is 15 pancakes, how many pancakes are actually produced?

Accepted Answer

11 pancakes

Question 6

For the reaction $$Ti(s) + 2\ Cl_2$(g) \rightarrow $$TiCl_4$$(s)$$, if you start with 1.8 mol $$Ti$$ and 3.2 mol $$Cl_2$$, what is the limiting reactant?

Accepted Answer

$$Cl_2$$

Question 7

Which of the following is true for an exothermic reaction?

Accepted Answer

Energy flows out of the system and $$\Delta H_{rxn} is $$negative.

Question 8

Calculate the percent yield if the actual yield of $$NaCl is 86.4 g $$and the theoretical yield is 92.0 g.

Accepted Answer

$$94\%$$

Question 9

Which equation correctly represents the enthalpy change for the combustion of methane?

Accepted Answer

$$CH_4(g) + 2$$\ $$O_2(g$$) \rightarrow $$CO_2(g) + 2$$\ H_2O(g)\ \Delta H_{rxn} = -802.3\ kJ$$

Question 10

If 11.8 $$	imes$$ $$10^3 g of $$propane ($$C_3H_8) is $$completely combusted, how much heat (in kJ) is released? (Molar mass $$C_3H_8 = 44.11 g/$$mol, $$\Delta H_{rxn} = -2044 kJ/$$mol)

Accepted Answer

$$547,000\ kJ$$

Question 11

Which of the following is a real-world consequence of incomplete combustion of octane in automobile engines?

Accepted Answer

Production of carbon monoxide and ozone as pollutants.

Question 12

What is the main reason ethanol is now used as a substitute for MTBE in gasoline?

Accepted Answer

Ethanol is biodegradable and does not contaminate drinking water.

Question 13

In the reaction $$Cu_2O(s) + C(s) \rightarrow 2\ Cu(s) + CO(g)$$, if you start with 11.5 g $$Cu_2O ($$molar mass = 143.10 g/mol) and 114.5 g $$C ($$molar mass = 12.01 g/mol), which is the limiting reactant?

Accepted Answer

$$Cu_2O$$

Question 14

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

Accepted Answer

The equation provides the mole ratios between reactants and products.

Question 15

If the world burns $$9.0 	imes 10$$^{12}$$ kg of octane per year, how much CO_2$ (in kg) is produced annually? (Use the balanced equation: 2$$\ C_8H_{18} + 25\ $$O_2$$ ightarrow 16\ $$CO_2 + 18$$\ H_2O$$; molar mass C_8H$$_{18}$$ = 114.22 g/mol, CO_2$ = 44.01 g/mol)

Accepted Answer

$$5.6 	imes 10$$^{13}$$ kg

Question 16

Which of the following is NOT a conversion factor commonly used in stoichiometry?

Accepted Answer

Density-to-density ratio for solids.

Question 17

Which scenario best illustrates the concept of a limiting reactant?

Accepted Answer

You have enough flour for 15 pancakes, enough eggs for 25 pancakes, and enough baking powder for 40 pancakes, but you can only make 15 pancakes.

Question 18

Which of the following statements about percent yield is correct?

Accepted Answer

Percent yield is the ratio of actual yield to theoretical yield, multiplied by 100%.

Stoichiometry and Quantities in Chemical Reactions

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