Reactions can only happens when particles collide, but not all end up in a reaction. Many particles bump off each other instead.
What does the collision theory state?
The collision theory states, the reactant particles must collide with each other and the collision needs to have sufficient energy in order for a reaction to occur.
In order for a reaction to happen, activation energy is needed.
Activation energy is the minimum amount of energy needed for particles collide successfully.
What is Activation Energy?
This is a diagram of the reaction between calcium carbonate and hydrochloric acid.
Only the particles on the surface are available for collisions. The frequency of successful collisions increases as the surface area of the solid increases.
What is a successful collision?
Successful collisions are collisions with energy greater than or equal to the activation energy.
Changing the temperature of the reaction causes the reaction to speed up or slow down depending on whether the temperature is increased or decreased.
Increasing the pressure of the reaction, makes no difference to the rate of reaction if it is a solid or liquid. However, increasing the pressure in a gas speeds up the reaction. The forces the particles closes together, so the collide more frequently. This is exactly the same as increasing the concentration of the gas.
Concentration of ReactantsReducing the concentration of the acid, makes the reaction slower.