Ch 6 Chemical Kinetics

Question 1

Chemical kinetics is the study of

Answer 1

the factors affecting the rate of a chemical reaction

Question 2

Rate of chemical reaction (definition) (3)

Answer 2

• the increase in the concentration of one of the products per unit time
• or the decrease in the concentration of one of the reactants per unit time
• dm-3 s-1

Question 3

Change in concentration can be measured by (2)

Answer 3

• measuring any property that differs between the reactants and the products
• e.g. using data loggers: mass/volume change (gas evolved), colour change, pH change (acidity), electrical conductivity (change in ionic concentration)

Question 4

Rate of reaction at any stated point in time using graph

Answer 4

gradient of the graph at that time

Question 5

Over time, rates of reaction usually

Answer 5

decrease as the reactants are used up

Question 6

Maxwell-Boltzmann Distribution (3)

Answer 6

• moving particles in a gas or liquid do not all travel with the same velocity
• faster moving particles possess more kinetic energy
• the distribution of kinetic energies is shown by a Maxwell-Boltzmann curve.

Question 7

Maxwell-Boltzmann curve: temperature increases (2)

Answer 7

• area under curve does not change because total number of particles remains constant
• more particles have higher velocity resulting in the increase in the average kinetic energy, which broadens the curve

Question 8

Collision theory: 3 conditions

Answer 8

• particles must collide
• they must collide with the appropriate geometry or orientation so that the reactive parts of the particles come into contact with each other
• they must collide with sufficient energy to bring about the reaction

Question 9

activation energy

Answer 9

minimum amount of energy required to start the reaction

Question 10

factors affecting the rate of reaction: temperature (3)

Answer 10

• particles will move faster as temperature increases so there will be more collisions per second
• more of the colliding particles will possess the necessary activation energy resulting in more successful collisions
• an increase of 10 degrees C will double the rate of a reaction

Question 11

factors affecting the rate of reaction: surface area (2)

Answer 11

• only particles on the surface of a solid substance can come into contact and react with a surrounding reactant
• solid in powdered form increases its surface area so rate increases

Question 12

factors affecting the rate of reaction: concentration (2)

Answer 12

• there will be more collisions per second per unit volume when the reactants are more concentrated
• concentration decreases as reactants get used up

Question 13

factors affecting the rate of reaction: catalyst (4)

Answer 13

• catalysts increase rate of chemical reaction without being chemically changed at the end of the reaction themselves
• bring the reactive parts of the reactant particles into close contact with each other
• provides an alternative pathway for the reaction with a lower activation energy
• most of the reactants will possess this lower activation energy, so the rate increases