Understanding Reaction Rate Factors

What happens to the rate of a chemical reaction when the temperature is increased?

• The reaction rate decreases

• The reaction rate increases

• The reaction rate remains the same

• The reaction stops completely

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

• It increases the activation energy required for the reaction

• It is consumed during the reaction to produce more products

• It lowers the activation energy without being consumed in the reaction

• It decreases the temperature of the reaction

Increasing the concentration of reactants in a solution generally causes the reaction rate to:

• Decrease, because there are fewer collisions between particles

• Increase, because there are more frequent collisions between particles

• Remain unchanged, because concentration does not affect reaction rate

• First increase, then decrease immediately

Which of the following statements about surface area and reaction rate is correct?

• Decreasing surface area increases the reaction rate

• Surface area has no effect on reaction rate

• Increasing surface area increases the reaction rate

• Surface area only affects reactions involving gases

In reactions involving gases, increasing the pressure causes the reaction rate to increase because:

• The gas molecules move slower at higher pressures

• The gas molecules are forced closer together, increasing the frequency of collisions

• Higher pressure decreases the concentration of gas molecules

• Pressure increases the activation energy of the reaction

A student is comparing two experiments. In Experiment A, a marble chip is placed in hydrochloric acid. In Experiment B, the same mass of powdered marble is placed in the same concentration of hydrochloric acid. Which experiment will have a faster reaction rate and why?

• Experiment A, because larger pieces have more mass

• Experiment B, because powdered marble has a greater surface area, allowing more collisions with acid particles

• Both experiments will have the same reaction rate because the mass is equal

• Experiment A, because larger pieces are more reactive than powder

According to the collision theory, which of the following best explains why increasing the temperature increases the reaction rate?

• Higher temperatures reduce the number of reactant particles present

• Higher temperatures give particles more kinetic energy, leading to more frequent and more energetic collisions that exceed the activation energy

• Higher temperatures increase the activation energy needed for the reaction

• Higher temperatures cause reactant particles to slow down and collide more precisely

A chemist is running a reaction between two gases at a fixed temperature. She doubles the pressure of the system. Based on your understanding of pressure and concentration, what is the most likely effect on the reaction rate?

• The reaction rate will halve because the molecules have less space to move

• The reaction rate will remain the same because temperature was not changed

• The reaction rate will increase because doubling the pressure effectively doubles the concentration of gas molecules, increasing collision frequency

• The reaction rate will decrease because higher pressure slows down molecular movement

Two students are dissolving sugar in water. Student A uses a sugar cube, while Student B crushes the sugar into fine powder before dissolving. Both use water at the same temperature. Student B's sugar dissolves significantly faster. Which explanation best accounts for this observation?

• Crushed sugar has a higher chemical reactivity than a sugar cube

• Crushed sugar has a greater surface area exposed to water molecules, increasing the rate of contact and dissolution

• The sugar cube contains more sugar than the crushed powder

• Crushing the sugar increases its temperature, which speeds up dissolution

• The catalyzed reaction is faster because the catalyst increases the concentration of reactants

• The catalyzed reaction is faster because the catalyst provides an alternative reaction pathway with a lower activation energy, increasing the number of successful collisions

• The uncatalyzed reaction is faster because the catalyst absorbs energy from the reaction

• Both reactions proceed at the same rate because the temperature and concentration are identical