rate and extent of chemical change

what two ways can rate of reaction be measured

• how fast a reactant is used up

• how fast a product is made

what methods determine the rate of reaction

1. mass loss

2. gas collection

3. precipitation

mass loss experiment

when a gas is produced in a reaction, it usually escapes from the reaction vessel, so the mass decreases

• mass measured every few seconds

• typically conical flask over a balance

• cotton wool in the neck to allow gas but no materials leaving

gas collection experiment

when a gas is produced in a reaction, it can be trapped and its volume measured over time

• volume of gas produced over time is recorded

• one gas collection set up involved collecting a gas through water using an inverted measuring cylinder

precipitation experiment

precipitation reactions form a solid precipitate when two clear solutions are mixed

the precipitate clouds the reaction mixture so flask placed over a cross

what is wrong with the dissapearing cross experiment

the method is susceptible to error as it is subjective

only one data point is produced so rate of reaction graph can be plotted

factors that affect the rate of reaction

1. concentration

2. temperature

3. surface area

4. catalyst

why do we want a higher rate of reaction

economic interest

higher rate of production, more efficient and sustainable process

collision theory definition

chemical reactions occur only when the reactant particles collide with sufficient energy to react

what affects the rate of reaction in terms of particles

1. number of particles per unit volume

2. frequency of collisions

3. kinetic energy of the particles

4. activation energy

how does increasing concentration affect rate of reaction

• more reactant particles in a volume

• more collisions per second

• more frequent and successful collisions

How does increasing pressure affect rate of reaction

• same particles in a smaller volume

• more collisions per second

• more frequent and successful collisions

how does temperature affect rate of reaction

increasing temperature means particles have more kinetic energy, more collisions

how does surface area affect rate of reaction

greater surface area of particles will be exposed to the other reactant, more collisions

catalyst definition

substances that speed up the rate of a reaction without themselves being altered or consumed in the reaction

how do catalysts work

• provide an alternative pathway for the reaction to occur

• alternative pathway has a lower activation energy

equilibrium definition

when a reversable reaction occurs in a closed system , equilibrium is reached when the reactions occur at exactly the same rate in each direction

what does the relative amount of the products and reactions depend on

the conditions of the reaction

describe le chateliers principle

when a change is made to the conditions of a system at equilibrium, the system automatically moves to oppose the change

describe pressure in le chateliers principle

if pressure increased, the position moves in the direction that has the smallest amount of gas molecules

what happens in le chateliers principle when the position moves to the right

if the forward reaction is favoured

there is then an increase is product formed

what happens in le chateliers principle when the position moves to the left

when the reverse reaction is favoured

increase in the reactants formed

how does increasing concentration affect equilibrium

• equilibrium shifts to the right

• reduces the effect of increasing the concentration of a reactant

• makes more product

how does decreasing concentration affect equilibrium

• equilibrium shifts to the left

• reduces the effect of decreasing the concentration of a reactant

• this makes less product

how does temperature affect equilibrium

increase: moves to endothermic reaction

decrease: moves to the exothermic reaction

how does pressure affect equilibrium

increase: favours reaction that produces the least number of molecules

decrease: favours the reaction that produces the greatest number of molecules