C5. Kinetics

Question 1

What is rate of reaction?

Answer 1

Change in concentration of product or reactant per unit time

Question 2

Whats the equation for rate of reaction?

Answer 2

Change in conc / Time , mol dm-3 s-1

Question 3

What is activation energy (Ea)?

Answer 3

Minimum energy required for successful collisions to take place and hence start a reaction, amount of energy required to start breaking bonds

Question 4

What are the factors needed for particles to react?

Answer 4

Enough energy, activation energy; Correct orientation

Question 5

What is the Maxwell Boltzmann distribution?

Answer 5

Describes molecular energies in gases

Question 6

What are the laws for Maxwell Boltzmann curves?

Answer 6

Particles in any substance are all moving at different speeds; No particles have no energy , curve begins at origin; No upper limit to energy a particle can have, curve never meets x-axis; Average energy is not equal to probable energy

Question 7

How do you calculate particle total from Maxwell Boltzmann curves?

Answer 7

Total area under graph

Question 8

What effects do increased temperature have on Maxwell Boltzmann curves?

Answer 8

Increasing temperature: increased speed and kinetic energy of particles, increased number of successful collisions per unit time; Graph shifts right, more particles have Ea

Question 9

What effects does increased pressure and concentration have on Maxwell Boltzmann curves?

Answer 9

Increased number of particles in given volume; increased number of successful collisions per unit time; Graph shifts left; as more particles collide and are used frequency of collisions decrease; hence rate decreases at end

Question 10

What effects does increased surface area have on Maxwell Boltzmann curve?

Answer 10

Increased area of solids, increases number of particles available to collide, hence increased frequency of successful collisions per unit time

Question 11

What is a chemical catalyst?

Answer 11

Substance that increases rate of a chemical reaction without being changed in chemical composition or amount

Question 12

How do catalysts work?

Answer 12

Provide an alternative reaction route of lower activation energy

Question 13

What is the effect of a catalyst on a Maxwell Boltzmann curve?

Answer 13

Proportion of particles that have Ea is increased, Ea line is shifted left

Question 14

Why are honeycomb meshes used for catalysts?

Answer 14

Increase surface area

Question 15

How does adsorption work in cars?

Answer 15

Gases in exhaust fumes attach to metal surface with weak bonds; weak bonds hold them in position in correct orientation; gases react on surface

Question 16

How does desorption work in cars?

Answer 16

Gases have reacted; particles detach from metal surface, leaving space for new particles; hence catalyst not used up

Question 17

What are the practical methods for measuring rates?

Answer 17

Time taken for precipitate to form; change in mass; Measure gas volume

Question 18

What is the practical for Time taken for precipitate to form?

Answer 18

Iodine clock; sodium thiosulfate reacting with hydrochloric acid; Stand conical flask over white surface with black cross; Add reactants; start stopwatch; Time taken for cross to no longer be visible

Question 19

What is the practical for change in mass?

Answer 19

Production of gas; Zn + H2SO4; Place conical flask on mass balance; place reactants in, start timer, place cotton ball at entrance; record mass at regular timed intervals until reaction ends

Question 20

What is the practical for measuring gas volume?

Answer 20

Rate of H2 production; Mg + HCl; Reactants in conical flask connected to gas syringe; record mass at regular timed intervals