Kinetics and Equilibria

Question 1

Rate

Answer 1

A measure of how fast a reaction proceeds.

Question 2

Collision/Particle theory

Answer 2

A reaction occurs when particles collide with enough energy/speed (Activation Energy, Ea) to react. The more collisions per second, the higher the rate.

Question 3

Activation Energy, Ea

Answer 3

The minimum amount of kinetic energy required in a collision for particles to react.

Question 4

What are the 4 factors that the rate of reaction depends on?

Answer 4

1) Temperature: if you increase the temp, particles move faster, so particles have more energy, so increased collisions, so increased rate. 2) Concentration (pressure): if you increase concentration: more particles, so more collisions, so increased rate. 3) Surface area: if you increase the surface area, more particles available to collide, so more collisions, so increased rate. 4) Catalyst: • Lowers the Ea requires for a successful collision, so increased successful collisions, so increased rate. • It provides a “site”/surface for particles to “stick” to. Increased the frequency of collisions, so increased rate.

Question 5

What are the advantages, and disadvantages of catalysts?

Answer 5

Advantages: • They reduce the temperature required for a successful reaction. This saves energy, time, and money. Disadvantages: • They are reaction-specific: you need a different one for each reaction. • Very expensive. • They can be destroyed/poisoned by impurities in a reaction.

Question 6

Rate (equation)

Answer 6

Rate = Amount of reactants (or products)/Time On a graph: • The steeper the gradient, the quicker the rate (because of temp/SA/catalyst) • The different rates should all level out at the same point (when all the reactants are used up). If there is a line that continues reacting, it had more reactants (higher concentration).

Question 7

Measuring rate: Precipitation reactions

Answer 7

(See diagram) Rate can be calculated by how quickly the X disappears. • The quicker it disappears, the quicker the reaction. • Make sure the same person does it each time (eyesight- some may see through cloudiness quicker).

Question 8

Measuring rate: Change in mass

Answer 8

(See diagram) Rate can be measured by timing how quickly mass falls. • The quicker the mass falls, the quicker the reaction. • Caution: gas is released into the room (do in a fume cupboard) • This is very accurate.

Question 9

Measuring rate: Volume of gas given off

Answer 9

(See diagram) Rate can be measured by how quickly a fixed volume of gas is produced. • More gas given off = faster reaction • Caution: if the reaction occurs too quickly it could disconnect the gas syringe… explode. • Gas syringes are quite accurate (to nearest mm)

Question 10

Exothermic reaction

Answer 10

Heat energy is transferred to surroundings (temp rises) from the bonds. e.g. Combustion (burning fuels), Neutralisation (acid + alkali), Oxidation reactions (e.g. Na + H2O) Uses: handwarmers, self-heating coffee cans

Question 11

Endothermic reaction

Answer 11

Heat energy is taken in from the surroundings (temp falls), and converted into bond energy. e.g. Thermal decomposition (e.g. CaC03 -> CaO + CO2) Uses: ice packs (for sports injuries)

Question 12

Maxwell-Boltzmann Distribution

Answer 12

Question 14

Maxwell-Boltzmann Distribution with Catalyst

Answer 14

Question 15

Maxwell-Boltzmann Distribution with temperature change

Answer 15

Question 16

Catalysts

Answer 16

A catalyst increases the rate of reaction by providing an alternativereaction pathway with a lower activation energy. The catalyst is chemically unchanged at the end of the reaction. They don’t get used up in the reaction.

Question 17

Le Chetalier’s Principle

Answer 17

If you change the concentration, pressure or temperature, the position of equilibrium moves to counteract the change.

Question 18

Catalysts and dynamic equilibrium

Answer 18

Catalysts have no effect on the position of equiibrium nor yield, but equilibrium is reahed faster.