Topic 9- Rates of reaction - Nadia Qureshi | Laabri

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1

According to collision theory, a chemical reaction occurs only when reactant particles collide with:

the products and the correct orientation

any amount of energy and any orientation

a catalyst and low pressure

sufficient energy and the correct orientation

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1

Which change increases the rate of a reaction by increasing the frequency of collisions (not necessarily the percent of successful collisions)?

Lowering the temperature

Adding a catalyst

Using larger chunks of a solid reactant

Increasing reactant concentration

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1

Why does increasing temperature generally increase the rate of a chemical reaction?

It increases kinetic energy so more collisions have enough energy to react

It decreases the activation energy of the reaction

It forces particles farther apart, preventing ineffective collisions

It increases the molar mass of reactant particles

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1

Which change increases reaction rate by increasing the surface area of a solid reactant?

Using a less reactive catalyst

Cooling the reaction mixture

Decreasing reactant concentration

Grinding the solid into a powder

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1

For a reaction involving gases, increasing pressure typically increases reaction rate because it:

decreases the number of gas particles in the container

forces gas particles closer together, increasing collision frequency

changes the identity of the reactants into more reactive gases

increases the distance between gas particles

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1

A reaction has a high activation energy barrier. Which change would most directly increase the percent of successful collisions without necessarily increasing the total number of collisions per second?

Use larger pieces of a solid reactant

Decrease the pressure of reacting gases

Add a catalyst

Increase the volume of the container

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2

Two experiments are run for the same reaction mixture. In Experiment A, the temperature is increased while all concentrations are kept the same. In Experiment B, a catalyst is added at the original temperature. Which statement best describes what changes in each case?

A increases concentration; B increases pressure

A increases $E_a$; B decreases $E_a$

A changes the reaction enthalpy; B changes the equilibrium constant

A increases the fraction of collisions with $E \ge E_a$; B provides a pathway with lower $E_a$

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1

A student increases the pressure in a sealed container where two gases are reacting. The reaction rate increases immediately. Which explanation best matches collision theory?

Higher pressure decreases activation energy by changing the reaction pathway.

Higher pressure changes reactants into more reactive substances.

Higher pressure decreases the average distance between gas particles, increasing collision frequency.

Higher pressure increases average kinetic energy, so every collision is successful.