$$\text{Rate} = \frac{\text{Change in reactant concentration}}{\text{Change in time}}$$

Question 1

Which of the following best describes the process shown in the first image (liquid water turning into steam)?

Accepted Answer

A physical change, because the state of H$$_2O $$changes but its chemical identity remains the same.

Question 2

Which equation correctly represents the rusting of iron, as shown in the image of rusty nails?

Accepted Answer

$$4Fe + 3O_2 \rightarrow 2Fe_2O_3$$

Question 3

Which of the following is NOT a requirement for a chemical reaction to occur according to collision theory?

Accepted Answer

Reactants must be in the gaseous state.

Question 4

Given the reaction: $$2Mg(s) + O_2$(g) \rightarrow 2MgO(s)$$, which of the following statements is true?

Accepted Answer

This is a chemical change because new substances are formed.

Question 5

Which factor would NOT increase the rate of a chemical reaction?

Accepted Answer

Decreasing the temperature.

Question 6

A catalyst affects a chemical reaction by:

Accepted Answer

Lowering the activation energy and speeding up the reaction.

Question 7

Which of the following best describes an exothermic reaction?

Accepted Answer

The energy of the products is lower than the reactants, and energy is released.

Question 8

Which of the following equations represents the rate of a chemical reaction in terms of reactant concentration?

Accepted Answer

$$	ext{Rate} = \frac{	ext{Change in reactant concentration}}{	ext{Change in time}}$$

Question 9

In an experiment, 0.5 g of marble chips (CaCO$$_3) $$are crushed and reacted with HCl. The reaction is faster than with whole chips because:

Accepted Answer

Crushed chips have a larger surface area, increasing the frequency of collisions.

Question 10

Which of the following best describes the energy profile of an endothermic reaction?

Accepted Answer

The energy of the products is higher than the reactants.

Question 11

Which symbol in a chemical equation indicates that the reactants are heated?

Accepted Answer

$$\Delta$$

Question 12

Which of the following scenarios is an example of a physical change?

Accepted Answer

Tearing a piece of paper in half.

Question 13

Which of the following will increase the rate of reaction between magnesium and hydrochloric acid?

Accepted Answer

Increasing the temperature of the solution.

Question 14

Which of the following is true about catalysts?

Accepted Answer

They lower the activation energy required for the reaction.

Question 15

Which of the following diagrams (I, II, III) best represents an endothermic reaction?

Accepted Answer

II and III

Question 16

If the activation energy ($$E_a) $$for a reaction is decreased, what will happen to the reaction rate?

Accepted Answer

The reaction rate will increase.

Question 17

Which of the following is a correct statement about the effect of temperature on reaction rate?

Accepted Answer

Increasing temperature increases the reaction rate by providing more energy for collisions.

Question 18

Which of the following is NOT a factor that affects the rate of a chemical reaction?

Accepted Answer

Color of the reactants

Question 19

Which of the following best describes the role of activation energy in a chemical reaction?

Accepted Answer

It is the minimum energy required to break bonds in the reactants.

Question 20

Which of the following best explains why increasing the surface area of a reactant increases the reaction rate?

Accepted Answer

It increases the number of collisions between reactant particles.

Chemical Changes, Chemical Reactions, and Reaction Rates: Foundations for Biochemistry

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