Chapter 12

When 1 g of a metal is oxidized, the resulting oxide has a mass that is a. less than 1 g b. equal to 1 g c. more than 1 g d. any of these, depending on the metal

C

When something burns, a. it combines with phlogiston b. it gives off phlogiston c. it combines with oxygen d. it gives off oxygen

C

A chemical reaction that absorbs energy is called a. endothermic b. exothermic c. activated d. oxidation-reduction

a

An example of an endothermic reaction is a. the dissociation of a salt in water b. the neutralization of an acid by a base c. the freezing of water d. combustion

a

An oxygen atom has a mass of 16.0 u. The number of moles of molecular oxygen, O2, in 64 g of oxygen gas is a. 2 b. 4 c. 32 d. 64

a

In round numbers the atomic mass of nitrogen is 14 u and Avogadro's number is N0 = 6 × 1023 formula units/mol. One mole of molecular nitrogen, N2, contains a. 6 × 1023 molecules b. 12 × 1023 molecules c. 84 × 1023 molecules d. 168 × 1023 molecules

a

When a gas reaction involves a decrease in the total number of molecules, the equilibrium can be shifted in the direction of higher yield by a. increasing the pressure b. decreasing the pressure c. increasing the temperature d. decreasing the temperature

a

When a substance gains electrons in a chemical reaction, the substance is said to be a. reduced b. oxidized c. electrolysed d. activated

a

At equilibrium, a. both forward and reverse reactions have ceased b. the forward and reverse reactions are proceeding at the same rate c. the forward reaction has come to a stop, and the reverse reaction is just about to begin d. the mass of reactants equals the mass of products Answer

b

If a given reaction is exothermic, the reverse reaction a. is exothermic b. is endothermic c. may involve no energy change d. any of these, depending on the reactio

b

The atomic mass of helium is 4.0 u and that of carbon is 12.0 u. a. The mass of 1 mole of carbon is 1/3the mass of 1 mole of helium. b. The mass of 1 mole of carbon is 3 times the mass of 1 mole of helium. c. One mole of carbon contains 1/3 as many atoms as 1 mole of helium. d. One mole of carbon contains 3 times as many atoms as 1 mole of helium. Answer

b

The chief constituent of dry air is a. oxygen b. nitrogen c. carbon dioxide d. argon

b

The formula mass of gaseous carbon dioxide, CO2, a. is 28 u b. is 44 u c. is 56 u d. depends on the mass of the sample

b

The mass of 1 mole of molecular nitrogen is a. 14 g b. 28 g c. 84 × 1023 g d. 168 × 1023 g

b

The mass of 6 × 1023 molecules of N2 is a. 14 g b. 28 g c. 84 × 1023 g d. 168 × 1023 g

b

The neutralization of a strong acid by a strong base a. absorbs energy b. liberates energy c. involves no energy change d. requires a catalyst to occur

b

The speeds of reactions between ions in solution a. depend critically upon temperature b. are essentially independent of temperature c. depend upon which catalyst is used d. are slow in general

b

The yield of the product C in the reversible reaction A+ B + energy C can be increased by a. decreasing the temperature b. increasing the temperature c. increasing the surface area of the reactants d. changing the catalyst Answer

b

A catalyst affects which one or more of the following? a. the energy needed for a chemical reaction to occur b. the energy a chemical reaction gives off c. the speed of a chemical reaction d. whether a substance is oxidized or reduced in a chemical reaction Answer

c

Batteries and fuel cells employ a. oxidation reactions only b. reduction reactions only c. both oxidation and reduction reactions d. acid-base neutralization reactions

c

How many moles of H atoms are present in 1 mol of H2O? a.1/2 b. 1 c. 2 d. 3

c

Reaction rates increase with temperature primarily because a. dissociation into ions is more complete b. more collisions occur between the molecules involved c. more activated molecules are formed d. equilibrium does not occur at high temperatures Answer

c

Six moles of O2 are consumed in a certain run of the reaction 2H2S + 3O2 → 2H2O + 2SO2. The number of moles of water produced in the run is a. 1 b. 2 c. 4 d. 6

c

The energy change in a chemical reaction depends on a. the bond energies of the reactants b. the bond energies of the products c. both of the above d. neither of the above

c

When a catalyst promotes a chemical reaction, it usually does so by a. providing energy b. providing electrons c. producing activated molecules d. becoming permanently altered

c

When an electric current is passed through molten sodium chloride, a. sodium metal is deposited at the positive electrode b. sodium ions are deposited at the positive electrode c. chlorine gas is liberated at the positive electrode d. chlorine ions are liberated at the positive electrode Answer

c

A fuel cell does not require a. a positive electrode b. a negative electrode c. oxidation-reduction reactions d. recharging

d

A mole of any compound contains Avogadro's number of a. atoms b. ions c. molecules d. formula units

d

A substance of unknown composition is heated in an open container. As a result, a. its mass decreases b. its mass remains the same c. its mass increases d. any of these can occur, depending on the nature of the substance and the temperature reached

d

For a reaction that occurs near room temperature, an increase of 10°C a. has little effect on the reaction speed b. increases the reaction speed by about 10 percent c. increases the reaction speed by about 50 percent d. approximately doubles the reaction speed

d

One mole of an element has a mass equal to a. Avogadro's number b. its atomic number expressed in grams c. its mass number expressed in grams d. its atomic mass expressed in grams

d

One mole of which of the following compounds contains the greatest mass of bromine? a. HBr b. Br2 c. AlBr3 d. SiBr4

d

The number of moles of carbon present in 3 mol of glucose, C6H12O6, is a. 2 b. 3 c. 6 d. 18

d

The quantity actually stored in a storage battery is a. electric charge b. electric current c. voltage d. energy

d

When the temperature at which a certain reversible reaction occurs is increased, the final amount of the reaction product(s) a. increases b. remains the same c. decreases d. does any of the above, depending on the reaction Answer

d