Rates

Question 0

Collision theory

Answer 0

A reaction occurs when reacting particles collide, & collide with enough energy to cause a reaction (Ea) and with the correct orientation.

Question 1

Rate of reaction

Answer 1

The change in concentration of a reactant or product in a given time.
Units: moldm^-3s^-1

Question 2

Effect of changing concentration

Answer 2

(n.b total volume is kept constant)

Increase concentration, so higher frequency of collisions, so faster rate.

Question 3

Increase in pressure

Answer 3

Less volume, so molecules collide more often as they’re pushed closer together. Therefore increase in rate.

Question 4

Change in temperature

Answer 4

As temperature increases, rate increases.

Note: only factor that changes the KE of the particles, which in turn influences rate.

Question 5

Catalyst

Answer 5

A substance that increases the rate of reaction without being used up by the overall reaction, by providing an alternative action route with a lower Ea.

Question 6

Heterogeneous catalysis

Answer 6

A reaction where the catalyst is in a different physical state to the reactants.
Most commonly: gaseous reactants & a solid catalyst. The catalyst works by adsorbing the reactants onto its surface, allowing them to react and then desorbing the products.

Question 7

Homogeneous catalysis

Answer 7

A reaction where the catalyst is in the same physical state to the reactants.
Most commonly: all gases/all liquids

Question 8

Maxwell-Boltzmann distribution

Answer 8

• graph of all the molecular energies of reacting particles at a particular temperature.
• area under the curve is the total number of particles in the sample.
• no molecules have 0 energy.
• there’s no max energy, so the curve gets v close to the x-axis
• only molecules with more energy than Ea can react