Balance this equation: H 2 (g) + N 2 (g)  NH 3 (g)

Balance this equation: ____ H2 (g) + ____ N2 (g)  ____ NH3 (g) A. 2, 2, 3 B. 2, 2, 5 C. 3, 3, 2 D. 3, 1, 2

Balance this equation: ____ P4 (s) + ____ H2 (g)  ____ PH3 (g) A. 4, 2, 3 B. 1, 6, 4 C. 1, 4, 4 D. 2, 10, 8

A refrigerator delays the spoilage of food by A. killing microorganisms. B. slowing the rate of chemical reactions within microorganisms. C. expanding the water found within microorganisms. D. diminishing the supply of oxygen to microorgansims.

The yeast in bread dough feeds on sugar to produce carbon dioxide. Why does the dough rise faster in a warmer area? There is a greater number of effective collisions among reacting molecules. Atmospheric pressure decreases with increasing temperature. The yeast tends to “wake up” with warmer temperatures, which is why baker’s yeast is best stored in the refrigerator. D. The rate of evaporation increases with increasing temperature.

Why does a glowing splint of wood burn only slowly in air but rapidly in a burst of flames when placed in pure oxygen? There is a greater number of collisions between the wood and oxygen molecules. Because oxygen is a flammable gas. Pure oxygen is able to absorb carbon dioxide at a faster rate. D. A glowing wood splint is actually extinguished within pure oxygen, because there’s no room for the smoke to expand.

What is the relationship between a hydroxide ion and a water molecule? A. A hydroxide ion is a water molecule plus a proton. B. A hydroxide ion and a water molecule are the same things. C. A hydroxide ion is a water molecule minus a hydrogen nucleus. D. A hydroxide ion is a water molecule plus two extra electrons.

Water is formed from the reaction of an acid and a base. Why is it not classified as a salt? Not all acid–base reactions produce salts, as in the case with the formation of water. The attraction between the two ions in water molecules is too strong. By definition, a salt must be able to dissolve in water, so water itself cannot be called a salt. D. A salt is an ionic compound, whereas water is a covalent compound.

What happens to the corrosive properties of an acid and a base after they neutralize each other? Why? The corrosive properties are neutralized, because the acid and base no longer exist. The corrosive properties are unaffected, because salt is a corrosive agent. The corrosive properties are doubled, because the acid and base are combined in the salt. D. The corrosive properties remain the same when the salt is mixed into water.

Cutting back on the pollutants that cause acid rain is one solution to the problem of acidified lakes. Suggest another. A. Stop using NaCl to salt the roads in the winter. B. Add a neutralizing substance such as limestone. C. Add ammonium ions to the lakes. D. Filter the water to remove any acidity in the lakes.

How might warmer oceans accelerate global warming? The evaporation of water from the ocean would increase significantly. The solubility of CO2 in water decreases as temperatures rise. The heat collected by the ocean water would be radiated back into the atmosphere. D. There would be less snow in the winter.

What element is oxidized in the following equation, and what element is reduced? I2 + 2 Br– 2 I– + Br2 A. iodine, I, is oxidized, while the bromine ion, Br–, is reduced. B. iodine, I, is reduced, while the bromine ion, Br–, is oxidized. C. both the iodine, I, and the bromine ion, Br–, are reduced. D. both the iodine, I, and the bromine ion, Br–, are oxidized.

What element behaves as the oxidizing agent in the following equation, and what element behaves as the reducing agent? I2 + 2 Br– 2 I– + Br2 A. The I2 is the oxidizing agent, while the Br– is the reducing agent. B. The I2 is the reducing agent, while the Br– is the oxidizing agent. C. The I- is the oxidizing agent, while the Br2 is the reducing agent. D. The I- is the reducing agent, while the Br2 is the oxidizing agent.

What element behaves as the oxidizing agent in the following equation and what element behaves as the reducing agent? I2 + 2 Br– 2 I– + Br2 A. The I2 is the oxidizing agent, while the Br– is the reducing agent. B. The I2 is the reducing agent, while the Br– is the oxidizing agent. C. The I- is the oxidizing agent, while the Br2 is the reducing agent. D. The I- is the reducing agent, while the Br2 is the oxidizing agent.

Ultraviolet Sun rays within the stratosphere cause oxygen molecules, O2, to transform into ozone molecules, O3. Is this an example of a physical or a chemical change? 3 O2 + UV  2 O3 A. Physical, because there are still only oxygen atoms. B. Chemical, because the oxygen atoms are bonded differently. C. Physical, because the Sun’s rays are a form of pure energy. D. Chemical, because energy is being absorbed.

Ultraviolet Sun rays within the stratosphere cause oxygen molecules, O2, to transform into ozone molecules, O3. Is this an example of an exothermic or an endothermic reaction? 3 O2 + UV  2 O3 A. Exothermic, because ultraviolet light is emitted. B. Endothermic, because ultraviolet light is emitted. C. Exothermic, because ultraviolet light is absorbed. D. Endothermic, because ultraviolet light is absorbed.

A friend argues that if mass were really conserved, he would never need to refill his gas tank. What explanation do you offer your friend? A. The Law of Conservation of Mass does not apply to reactions involving combustion or explosion of matter. B. The oil companies make gasoline in a way that it gets used up so that we are always required to replenish it. C. The atoms (mass) of gasoline are converted into energy by the engine according to E = mc2. D. The atoms (mass) of gasoline are converted into exhaust fumes.

Gasoline contains only hydrogen and carbon atoms. Yet nitrogen oxide and nitrogen dioxide are produced when gasoline burns. What is the source of the nitrogen and oxygen atoms? A. These atoms are from the impurities dissolved within the gasoline. B. Nitrogen oxide and nitrogen dioxide from the atmosphere are pulled into the combustion chamber prior to exiting the engine through the exhaust. C. Atmospheric nitrogen and oxygen react with each other within the combustion chamber. D. According to the principle of the conservation of mass, this is not possible.

How many diatomic molecules are represented in the chemical reaction shown below? A. 1 B. 2 C. 3 D. 4

The reactants shown schematically below represent iron oxide, Fe2O3, and carbon monoxide, CO. Which of the following is the correct full balanced chemical equation for what is depicted? A. Fe2O3 + 3 CO  2 Fe + 3 CO2 B. Fe2O3 + 3 CO  2 Fe + 3 C2O C. Fe2O3 + 3 CO  3 FeO2 + 2 C D. Fe2O3 + 3 CO  3 FeO + 2 C

Why does a glowing splint of wood burn only slowly in air but rapidly in a burst of flames when placed in pure oxygen? A. Pure oxygen is able to absorb carbon dioxide at a faster rate. B. A glowing wood splint is actually extinguished within pure oxygen, because there’s no room for the smoke to expand. C. There are a greater number of collisions between the wood and oxygen molecules. D. Oxygen is a flammable gas.

The warm air from a lit birthday candle does not rise within an orbiting space station because there is no up or down. As a result, what happens to the burning candle and why? A. The warm air surrounding the candle speeds up the rate of reaction so that the candle burns brighter. B. Soot from the candle forms a ball around the candle. The temperature inside this ball builds up until there is a small explosion. C. Less oxygen becomes available to the flame to the point the flame is extinguished. D. The candle continues to burn with nothing unusual happening.

Use the bond energies below to determine whether the following reaction is exothermic or endothermic: H2 + Cl2 2 HCl H-H bond energy: 436 kJ/mol H-Cl bond energy: 431 kJ/mol Cl-Cl bond energy: 243 kJ/mol A. Exothermic with more than 50 kJ of energy released. B. Endothermic with more than 50 kJ of energy absorbed. C. Endothermic with less than 50 kJ of energy absorbed. D. Exothermic with less than 50 kJ of energy released.

Identify the acid or base behavior of each substance in these reactions: H3O+ +Cl– H2O + HCl A. H3O acts as a base, Cl– acts as an acid, H2O acts as an acid, HCl acts as a base. B. H3O acts as a base, Cl– acts as an acid, H2O acts as a base, HCl acts as an acid. C. H3O acts as an acid, Cl– acts as a base, H2O acts as an acid, HCl acts as a base. D. H3O acts as an acid, Cl– acts as a base, H2O acts as a base, HCl acts as an acid.

When the hydronium ion concentration equals 10 moles per liter, what is the pH of the solution? Is the solution acidic or basic? A. pH = 1; this is an acidic solution. B. pH = 0; this is an acidic solution. C. pH = –0.301; this is an acidic solution. D. pH = 7; this is a neutral solution.

What happens to the pH of a 1M solution of hydrochloric acid, HCl, as a solution of 1M acetic acid is added to it? A. The pH remains unchanged. Acetic acid is a weak acid and unable to affect the pH in the presence of such a concentrated solution of such a strong acid. B. The pH of the solution decreases (becomes more acidic), because two acids are being combined. C. The pH of the solution increases (becomes less acidic), because the acetic acid solution is diluting the hydrochloric acid solution. D. None of the above.

Why are seasonal fluctuations in atmospheric CO2 much more pronounced in the northern hemisphere compared to the southern hemisphere? A. The trees and other photosynthetic plants absorb atmospheric carbon dioxide in summer in the northern hemisphere but lose their leaves in fall and winter, and photosynthesis stops. B. During the fall and winter in the northern hemisphere, decay of the organic matter generates carbon dioxide, which increases the atmospheric CO2 levels by the spring. C. Both A and B are true. D. CO2production is more limited in the area of our planet’s largest land masses, which are located in the southern hemisphere.

Balance this equation: H 2 (g) + N 2 (g)  NH 3 (g)