1. Which statement explains why the speed of some chemical reactions is increased when the surface area of the reactant is increased?

A)    This change exposes more reactant particles to a possible collision.

B)    This change increases the concentration of the reactant.

C)    This change increases the density of the reactant particles.

D)    This change alters the electrical conductivity of the reactant particles.

Correct Answer: Option A - This change exposes more reactant particles to a possible collision.

Reaction rate is affected by nature and concentration of reactants, temperature, surface area and a catalyst. Increasing surface area exposes more particles to contact with reactants, increasing the number of particle collisions.

For Example: Imagine a cube of chocolate 3 feet by 4 feet and 2 inches thick. Take the same block and make it into a 24 candy bars. A class of students could eat the bars faster than the single chocolate block.

Hence, options B, C and D are incorrect.

2. Which substance is produced by the Haber process?

A)    Sulfuric acid

B)    Nitric acid

C)    Ammonia

D)    Aluminum

Correct Answer: Option C - Ammonia

The Haber process, also called the Haber-Bosch process, is the nitrogen fixation reaction of nitrogen gas and hydrogen gas, over an enriched iron catalyst, to produce ammonia. The Haber process is important because ammonia is difficult to produce on an industrial scale, and the fertilizer generated from the ammonia is responsible for sustaining one-third of the Earth's population.

Hence, options A, B and D are incorrect.

Base your answers to questions 3, 4 and 5 on the reaction represented by the balanced equation below:

2H₂(g) + O₂(g) → 2H₂O(l) + 571.6 kJ

3. Identify the information in this equation that indicates the reaction is exothermic.

Correct Answer:

Heat term is on the right side of the equation.

The 571.6 kJ is a product.

The heat term expressed in kJ being on the right side of the equation indicates that the reaction is exothermic.

Base your answers to questions 3, 4 and 5 on the reaction represented by the balanced equation below:

2H₂(g) + O₂(g) → 2H₂O(l) + 571.6 kJ

Correct Answer:

The reaction is marked along the X axis and potential energy is marked on the Y axis. As the reaction proceeds the potential energy increases and then gradually decreases.

Base your answers to questions 3, 4 and 5 on the reaction represented by the balanced equation below:

2H₂(g) + O₂(g) → 2H₂O(l) + 571.6 kJ

Correct Answer:

Entropy (S) is a measure of the randomness or disorder of a system. Consequently, systems that are more chaotic have a higher entropy value. If a change makes a system more random, ΔS is positive. If a change makes a system more ordered, ΔS is negative.

Entropy of a system can decrease due to any one of the following reasons:

• A liquid is formed from gases.
• A compound is formed from its elements.
• The number of gas particles in the system decreases.

6. For a given reaction, adding a catalyst increases the rate of the reaction by

A)    Providing an alternate reaction pathway that has higher activation energy

B)    Providing an alternate reaction pathway that has lower activation energy

C)    Using the same reaction pathway and increasing the activation energy

D)    Using the same reaction pathway and decreasing the activation energy.

Correct Answer: Option B - Providing an alternate reaction pathway that has lower activation energy

Catalysis is the process in which the rate of a chemical reaction is either increased or decreased by means of a chemical substance known as a catalyst. Unlike other reagents that participate in the chemical reaction, a catalyst is not consumed by the reaction itself. The catalyst may participate in multiple chemical transformations. Catalysts that speed the reaction are called positive catalysts. Catalysts that slow down the reaction are called negative catalysts or inhibitors. Substances that increase the activity of catalysts are called promoters and substances that deactivate catalysts are called catalytic poisons. A catalyst works by providing an alternative reaction pathway to the reaction product. The rate of the reaction is increased as this alternative route has lower activation energy than the reaction route not mediated by the catalyst.

Hence, options A, C and D are incorrect.

7. Which term is defined as a measure of the average kinetic energy of the particles in a sample?

A)    Thermal energy

B)    Pressure

C)    Chemical energy

D)    Temperature

Correct Answer: Option D - Temperature

Kinetic Energy is the energy of motion.  Another kind of energy, Potential, or Static Energy, is the energy of position. Both energies are understood to refer to force acting upon matter. Together, these energies add up to a system's total energy, or

E (total) = E (potential) + E (kinetic)

Potential and Kinetic are convertible, one to the other. Kinetic energy can be defined in terms of mass (m) and velocity (v) of an object in the form

E (kinetic) = 1/2 mv²

The particles of matter (i.e. molecules) at non-extreme temperatures can be considered to have random velocity. Then the average translational kinetic energy (KE) for these molecules can be deduced by assuming that prob(KE=x) follows a Boltzmann distribution. The well known equation for kinetic energy follows:

average KE = [1/2 * m v²] = 3kT/2,

where m = mass, v = velocity, k = Boltzmann's constant, and T = Temperature

In other words, average KE is directly proportional to T.

Thermal energy, pressure and chemical energy are not the measures of kinetic energy. Hence, options A, B and c are incorrect.

8. A 5 gram sample of zinc and a 50 milliliter sample of hydrochloric acid are used in a chemical reaction. Which combination of these samples has the fastest reaction rate?

A)    Zinc strip and 1 M HCl(aq)

B)    Zinc powder and 3 M HCl(aq)

C)    Zinc strip and 3 M HCl(aq)

D)    Zinc powder and 1 M HCl(aq)

Correct Answer: Option B - Zinc powder and 3 M HCl(aq)

Zinc powder being in a smooth form and a large surface area along with a molarity of 3M being greater than the other combinations reacts fastest due to a higher surface area and higher molarity.

Hence, options A, C and D are incorrect.

9. State some methods to increase the rate of a chemical reaction and explain, in terms of particle behavior, how each method increases the reaction rate.

Correct Answer:

Some methods to increase the rate of chemical reaction are:

• Increasing the temperature of the reaction causes the reacting particles to move faster and collide more frequently.
• Increasing the concentration increases the number of particle collisions.
• Increasing the surface area (solid reactant) allows a greater number of particles to collide.
• Adding a catalyst provides an alternate way for the particles to react.

10. Given the equation representing a reaction at equilibrium:

N₂(g) + 3H₂(g) ↔ 2NH₃(g) + energy

Which change causes the equilibrium to shift to the right?

A)    Decreasing the concentration of H₂(g)

B)    Decreasing the pressure

C)    Increasing the concentration of N₂(g)

D)    Increasing the temperature

Correct Answer: Option C - Increasing the concentration of N₂(g)

Increasing the concentration of nitrogen gas aids, further reaction with hydrogen thus forming more ammonia and releasing more energy; shifting the reaction to the right.

Incorrect Options:

Decreasing the concentration of hydrogen will make lesser hydrogen available for the reaction causing the reaction to shift left. Hence, option A is incorrect.

Pressure is not involved in the reaction; hence, decreasing the pressure will not affect the reaction. Hence, option B is incorrect.

Increasing the temperature will increase the right side elements in the reaction, causing the reaction to shift left. Hence, option D is incorrect.