Chemistry Speed of Reaction

**Collision theory** states that in order for a reaction to occur,


1. The reactant particles must not only collide,
2. but must also collide with sufficient energy

State the definition of **collision theory**.

Frequency of effective collisions (number of successful collisions per unit time)

How is rate of reaction determined?

1. temperature
2. pressure (gaseous)
3. concentration (aqueous)
4. surface area (solid)
5. presence of a catalyst (selected reactions only)

Name the **five** factors affecting frequency of effective collisions

1. The higher the temperature, the faster the reactant particles move about.
2. Particles collide into each other **more often** and with greater force,
3. leading to an increase in the frequency of effective collisions.

Explain the factor of **temperature**

1. The higher the concentration of an aqueous solution, the greater the number of particles per unit volume.
2. Particles collide into each other more often
3. Leading to an increase in the frequency of effective collisions.

Explain the factor of **concentration**

1. The higher the pressure of a gas, the **greater** the number of particles per unit volume.
2. Particles collide into each other more often,
3. leading to an increase in the frequency of effective collisions.

Explain the factor of **pressure**

1. The smaller the particle size, the larger the surface area of contact between the reactant particles.
2. More particles collide into each other at a given time,
3. leading to an increase in the frequency of effective collisions

Explain the factor of **particle size**

A catalyst is a **substance** which increases the speed of a chemical reaction but itself remaining chemically unchanged at the end of the reaction.

What is a **catalyst?**

Catalysts provide an alternative reaction pathway of lower activation energy. More particles possess the required activation energy to collide more often, increasing the frequency of effective collisions.

How do catalysts increase speed of reaction?