Topic 6 - Chemical Kinetics

Question 1

What is the rate of reaction defined as?

Answer 1

• the change in concentration of reactants or products per unit time

Question 2

What are the 4 experimental measures of reaction rates?

Answer 2

• change in pH
• change in conductivity
• change in mass/volume
• change in colour

Question 3

What is the average rate defined as?

Answer 3

• a measure of the change in concentration of reactant or product in a given time interval, t

Question 4

What is the instantaneous rate?

Answer 4

• when t = t0, the instantaneous rate = the initial rate

- tangent of the curve

Question 5

What are the 4 kinetic-molecular theories of gases?

Answer 5

1) Gases consist of a huger number of particles, which are moving at high velocities in random directions.
2) The size of a gaseous particle is negligible (volumes), but have mass - due to large space between atoms.
3) Collisions between particles are entirely elastic. There is no net loss of energy.
4) The average kinetic energy of the particles is proportional to the absolute temperature (in K). The movement is due to their thermal energy. At a given moment, some will be moving at greater velocities than other. Increasing temperature also increases kinetic energy.

Question 6

What is a catalyst?

Answer 6

• a substance that increases the rate of a chemical reaction, but is not consumed in the reaction itself
• it provided an alternative pathway for the reaction and lower the activation energy
• does not change the enthalpy change of the original reaction without the catalyst

Question 7

What is a homogeneous catalyst?

Answer 7

• in the same physical phase as the reactants

Question 8

What is a hetreogeneous catalyst?

Answer 8

• in a different phase as the reactants

Question 9

What is the ozone layer?

Answer 9

• absorbs over 95% of UV radiation reaching the Earth (Sun)

Question 10

What is a catalytic converter?

Answer 10

• converts harmful exhaust chemicals into less harmful substances

Question 11

What effect does increasing temperature have on the kinetic energy?

Answer 11

• the proportion of the particles with sufficient energy to overcome Ea barrier increases
• the mean velocity increases
• proportion of particles with enough kinetic energy increases

Question 12

What are the 4 factors affecting the rate of a chemical reaction?

Answer 12

1) increasing temperature
2) adding catalyst
3) increasing concentration
4) decreasing particle size - increasing surface area