Unit 3 AOS 1 - Chapter 4: Rates of Chemical Reactions

What is collision theory?

A theoretical model that explains the rate of reaction in terms of collisions between particles.

What are successful collisions and what are the conditions required for a successful collision to occur?

Collisions that allow products to form. The conditions are:

1. The reactants physically collide

2. Reactants must collide with sufficient energy to break the bonds within them (the activation energy)

3. Must collide with correct orientation

Affect of temperature on rate of reaction

The temp. Of a substance is the average kinetic energy of the particles. Higher the temp, the more kinetic energy (more movement) leading to more collisions. Additionally, the number of reactants wit enough energy to surpass the activation energy increases, again increasing the rate of reaction

Affect of surface area on rate of reaction

The S.A of reactants referees to how much area a solid has available to collide with others. In the case of solid reactant samples, when its S.A increase, reactant particles can collide more frequently, resulting in more successful collisions over a given period of time and thus a faster rate of reaction.

How does concentration affect the rate of reaction?

Increase in conc. Means an increase in the particles per unit of volume. Therefore, collisions happen more frequently and there are more collision per unit of time, therefore the rate of reaction increases.

How does pressure affect the rate of reaction?

As volume decreases (increasing pressure and conc.), particles are in a smaller space, meaning more reactant particles per unit of volume. Therefore, collision frequency and collision per unit of time increase thus the rate of reaction increase

How can you measure the rate of reaction

Precipitation/colour change, change in mass, volume of gas given off, pH. Can be an open or closed system

Catalysts

Substances used to provide an alternative reaction pathway w/ a lower activation, thus decreasing the amount of energy required to break the bonds in the reactants, meaning a greater proportion of reactant particles have the sufficient energy to collide successfully. They are usually porous or powdered to increase surface area. They can be used in multiple reactions as they are not chemically altered.

Stuff abt catalysts

- work by temporarily binding to reactants which decreases the amount of energy required to break bonds

- do not increase % yield or yield, only the rate at which products r formed

- transition metals and compounds are commonly used as catalysts in industrial processes

Heterogenous Catalysts

Catalysts present in a different physical state to the reactants

Homogenous catalysts

Catalysts present in the same physical state as the reactants and products