NEED TO ADD BOLTZMAN CURVE FOR CATALYST

Reaction rate

Reaction rate is defined as the change in concentration (or amount) of a reactant or product over time.

A simple formula for finding the rate of a chemical reaction is:

What methods are used to measure reaction rates?

Measuring a decrease in mass

Measuring the volume of gas given off

Timing how long a precipitate takes to form

How do you calculate rate from a graph?

Plotting the amount of reactant used or product formed against time on a graph, the slope (or gradient) of the curve represents the reaction rate. A tangent may need to be drawn.

What is collision theory?

Collision theory states that for a reaction to occur between particles, two conditions must be met:

1. Orientation - The particles must collide in the correct orientation. They need to be facing each other appropriately.

2. Energy - The colliding particles need at least a minimum amount of kinetic energy. This minimum energy is called the activation energy (E_a).

What is the activation energy?

Minimum energy required for a collision to be effective. This energy is necessary to break existing bonds in the reactants and initiate the reaction. Particles with kinetic energies greater than or equal to the activation energy will have sufficient energy to react upon collision.

The 5 key factors that affect the rate of a chemical reaction are:

1. Surface area (of solids)

2. Concentration (of solutions)

3. Pressure (of gases)

4. Temperature

5. Catalyst

Effect of surface area on rate of reaction

Increasing surface area increases rate of reaction

• When the exposed surface area of the solid is increased, more particles on the surface are available to collide and react. This leads to a higher frequency of effective collisions between the solid and other reactants.

• For example, crushing a solid into a powder provides more exposed surface.

• Therefore, increasing the surface area of a solid reactant results in an increased reaction rate.

Effect of concentration on rate of reaction

Increasing concentration increases rate of reaction

• If the concentration of reactants in solution is increased, the particles will on average be closer together.

• Particles that are closer together will collide more frequently, increasing the number of effective collisions.

• Therefore, increasing the concentration increases the reaction rate.

Effect of pressure on rate of reaction

Increasing pressure increases rate of reaction

• Raising the pressure forces the gas particles closer together.

• Particles that are closer together will collide more frequently, increasing the number of effective collisions.

• Therefore, increasing the pressure increases the reaction rate.

Effect of temperature on rate of reaction

Increasing temperature increases rate of reaction

• Raising the temperature increases the kinetic energy and speed of the particles.

• As the particles move faster, they collide more frequently, resulting in an increased frequency of collisions.

• Additionally, the increased kinetic energy means more particles have the necessary energy to overcome the activation energy, resulting in a greater proportion of effective collisions.

• Therefore, increasing temperature results in an increased reaction rate.

Definition of a catalyst

A catalyst is a substance that increases the rate of a chemical reaction. It does this by providing an alternative route for the reaction that has a lower activation energy. Importantly, the catalyst itself is not consumed in the reaction; it temporarily participates in the reaction but is chemically regenerated at the end.

Effect of catalyst on rate of reaction

Adding a catalyst increases rate of reaction

• A catalyst provides an alternative pathway or mechanism for the reaction that has a lower activation energy.

• A lower activation energy means particles require less kinetic energy to react.

• More particles have the activation energy, leading to an increased number of effective collisions.

• Consequently, adding a catalyst increases the overall rate of reaction

What are the types of catalyst?

1. Heterogeneous catalysts

1. Homogeneous catalysts

Heterogeneous catalyst

1. These are in a different phase from the reactants.

• For example, in the Haber process, solid iron is used as a catalyst for gaseous nitrogen and hydrogen.

• The reaction takes place on the surface of the catalyst, so increasing the surface area can increase the rate of reaction.

Homogeneous catalysts

1. These are in the same phase as the reactants.

• Typically, these are aqueous catalysts used in reactions involving aqueous solutions.

• An example is sulfuric acid serving as a catalyst in the reaction between aqueous hydrogen peroxide and aqueous potassium iodide, where it works by forming intermediate species that lead to the final products.