Rates and Equilibrium

Reaction Rate

a measure of how quickly reactants and converted into products

Ways to measure reaction rate

• Change in temperature

• Change in mass

• Precipitate formed

• Change in colour

• Volume of gas evolved

• pH change

Requirements for a successful collision

1) reactants must physically collide with each other

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

3) Reactants must collide with the correct orientation for bonds to actually break

Effect of increasing temperature on rate of reaction

• Increases average kinetic energy of particles per unit volume

• therefore increases the proportion of particles with sufficient kinetic energy to overcome the activation energy

• thus a greater likelihood that particles will collide, increasing the number of successful collisions per unit time

• hence causing rate of reaction to increase

Effect of increasing concentration on rate of reaction

• Increases the number of particles per unit volume

• thus a greater likelihood particles will collide, increasing the number of successful collisions per unit time

• hence causing rate of reaction to increase

Effect of increasing pressure on rate of reaction

• Increases the number of reactant particles present per unit volume

• Therefore increasing the frequency of collisions between particles

• Thus increasing the proportion of successful collisions per unit time

• Hence an increased rate of reaction

Effect of increasing surface area on rate of reaction

• Greater number of particles exposed

• Therefore increases frequency of collisions per unit time

• Thus increases frequency of successful collisions

• Hence causing rate of reaction to increase

Effect of adding a catalyst on rate of reaction

• Catalyst lowers the activation energy

• Greater proportion of particles will have sufficient kinetic energy to overcome the activation energy

• Therefore a greater proportion of successful collisions will occur

• Hence causing rate of reaction to increase

Heterogeneous catalyst

Catalyst in a different state to reactants and products

Homogeneous catalyst

Catalyst in the same state as reactants and products

Specifics of catalysts in reactions

• change the RATE of reaction, NOT the YIELD

• Make a reaction go faster

• Do not take part in the reaction

• Are not changed during the reaction

• Are not used up in the reaction

• Does not effect enthalpy change

• Does not effect equilibrium

How to calculate Reaction Rate

change in amount of product/reactant divided by time taken

Exothermic reactions

• — enthalpy change

• Heat is produced

• reactant bonds have greater energy than product bonds

• energy is lost from the reactant bonds to the surrounding environment making it feel hotter

Endothermic reactions

• + enthalpy change

• Heat is absorbed

• product bonds have greater energy than reactant bonds

• energy is used for the product bonds from the surrounding environment making it feel colder

Closed system

a reaction system that does not gain or lose energy or matter from the outside

Open system

a system that can exchange matter and energy with its surrounding environment

LCP

According to LCP, if a system at equilibrium is subjected to a change, there will be a tendency for a net reaction in the direction that reduces the effect of this change.