3.2.2 Reaction Rates

Question 1

Effect of concentration on the rate of reaction

Answer 1

• as conc increases there are more particles per unit volume
• more collisions per second resulting in more reactions per second
• increase in the rate of reaction

Question 2

Effect of gas pressure on rate of reaction

Answer 2

• as pressure increases there are more particles per unit volume
• more collisions per second resulting in more reactions per second
  -increase in rate of reaction

Question 3

Effect of particle size on rate of reaction

Answer 3

• small particles have a larger surface area
• more collisions per second
• more collisions resulting a reaction
• rate of reaction increases

Question 4

Effect of temperature on rate of reaction

Answer 4

• particles have greater kinetic energy
• more collisions per second
• more collisions result in reactions
• more particles will have more energy than the activation energy

Question 5

What is the definition of rate of reaction?

Answer 5

Rate = change in concentration / time
moldm-3s-1

Question 6

What conditions must be satisfied for a chemical reaction to occur by collisions?

Answer 6

• must collide
• with sufficient kinetic energy
• in the correct orientation
• must have equal to or over the activation energy

Question 7

What is the activation energy?

Answer 7

The minimum amount of energy required for a chemical reaction to occur

Question 8

What is the role of a catalyst?

Answer 8

• increases reaction rate without being used up in the overall reaction
• allows a reaction to proceed on an alternative pathway with lower activation energy
• (therefore more particles have greater than the activation energy)

Question 9

What are heterogeneous catalysts?

Answer 9

• catalysts that are in a different phase as the reactants
• e.g. solid catalyst in liquid reaction
• e.g. solid iron in the Haber process to make gaseous ammonia
• nitrogen + hydrogen -> ammonia

Question 10

Why are catalysts important?

Answer 10

• great economic importance and benefits for increased sustainability
• by lowering temperatures and reducing energy demand from combustion of fossil fuels with resulting decrease in CO2 emissions

Question 11

What is a homogeneous catalyst?

Answer 11

• catalysts that are in the same phase as the reactants
• e.g liquid catalyst in a liquid reaction
• e.g. concentrated sulphuric acid added to an esterification reaction
• e.g. enzymes in body

Question 12

What is the Boltzmann distribution curve?

Answer 12

• shows how the energies of the particles are distributed in the sample or substance being used

Question 13

What are the rules of the Boltzmann distribution curve?

Answer 13

• no particles have no energy and no particles have the maximum amount of energy
• the curve never touches the axis (within 1/2 square of axis)a

Question 14

What is does the area under the Boltzmann distribution curve show?

Answer 14

• total area under the curve = total number of particles in sample
• area under graph greater than Ea = number of particles that can react - successful collisions per second

Question 15

Draw the Boltzmann distribution curve

Answer 15

See notes

Question 16

Draw the Boltzmann distribution curve with a catalyst (lower Ea)

Answer 16

See notes
More particles with energy greater than or equal to Ea, so more successful collisions per second

Question 17

Draw the Boltzmann distribution curve for lower, medium and higher temperature

Answer 17

See notes