chemical kinetics

Chemical kinetics

Rate of a reaction O 1) amount of reactant used up/time

taken O 2) amount of product formed/time

takenO 3) volume of gas produced/time

taken

Measuring rate of reaction –volume of gas produced O Since magnesium reacts with dilute

HCl to form hydrogen gas, the speed of reaction can hence be determined by measuring the volume of hydrogen gas produced at regular time intervals.

Experimentation Time! O Conduct your own experiment and

sketch out your own vol. of hydrogen vs time graph!

Graph analysisO Gradient of graph speed of

reactionO The steeper the gradient, the faster

the speed of reaction O Decrease in steepness indicates

decreasing speed of reaction O Shape of graph

changes/consistency in speed of reaction as time passes

Measuring speed of reaction-changes in massO Allow gas produced to escape and

measure the loss of massO Reaction speed determined by

measuring loss of mass at regular time intervals

Factors affecting rate of a chemical reaction

O Summary: O Temperature O Concentration O PressureO Surface area O Presence of a catalyst

Collision theory O For a reaction to occur, reacting

particles must O 1) collide with each other O 2) possess activation energy

O Note: Orientation of collision must be correct as well

Factor 1: Temperature O Increase in temp. increase in KE

increase in no. of collisions + increase in no. of particles with greater than required amount of activation energy more particles react increase rate of reaction

Put on your thinking cap!

O Can you explain why food should be kept in deep-freeze compartments in order to ensure its freshness?

O (answer on next slide)

O Answer: O The low temperature slows down

chemical reactions which makes the food turn bad.

Factor 2: Concentration/Pressure O High concentration/pressure more

particles per unit volume increase in frequency of collisions rate of reaction increases

Factor 3: Surface area O Increase in surface area/particle size

increase in exposure to the other reactant increase in probability of collisions increase in rate of reaction

Factor 4: Presence of Catalyst

O Speeds up rate of reaction through lowering activation energy needed for reaction to occur

O Think: What can you infer from the above statement?

The end Learn through understanding,

not through memorization.