Factors Affecting Rate (Temperature, Concentration, Surface Area, Pressure)

Effect of Temperature

Increasing the temperature makes particles move faster, so they have more energy. This means particles collide more often and with greater energy. Because of this, the number of successful collisions increases, speeding up the reaction.

For instance, when you heat a reaction mixture, the particles gain kinetic energy and collide more frequently and more forcefully, making the reaction go faster.

Example: If a reaction takes 60 seconds at 206C, increasing the temperature to 406C might reduce the time to 30 seconds because particles collide more often and with more energy. Note: This is an approximate example; actual changes depend on the reaction and activation energy.

Effect of Concentration

Increasing the concentration of a solution means there are more particles of the reactant in the same volume. This increases the chance of particles colliding per second, so the reaction rate increases.

For example, if you double the concentration of hydrochloric acid reacting with magnesium, the rate of reaction roughly doubles because there are twice as many acid particles to collide with magnesium.

Example: If a reaction with 1 mol/dm9 acid takes 50 seconds, increasing the acid concentration to 2 mol/dm9 might reduce the time to about 25 seconds. Note: This is a general approximation; the exact relationship depends on the reaction order.

Effect of Surface Area

For reactions involving solids, increasing the surface area exposes more particles to react. This means more particles are available to collide with other reactants, increasing the collision frequency and speeding up the reaction.

For example, powdered calcium carbonate reacts faster with acid than large lumps because the powder has a greater surface area.

Example: If a lump of marble takes 100 seconds to fully react with acid, the same mass as powder might react completely in 20 seconds.

Effect of Pressure

Pressure only affects reactions involving gases. Increasing the pressure compresses the gas particles into a smaller volume, increasing their density.

This means gas particles collide more frequently, increasing the rate of reaction.

For example, increasing the pressure in a reaction between hydrogen and nitrogen gases speeds up the formation of ammonia.

Example: If a reaction takes 60 seconds at 1 atmosphere, increasing the pressure to 2 atmospheres can reduce the time to about 30 seconds.