A4 kinetics 1

Question 1

what is activation energy?

Answer 1

heat energy required per mole for a collision between two particles to result in a chemical reaction.

Question 2

how should you think about rate?

Answer 2

rate = collision frequency x successfulness

Question 3

what factor affect collision frequency?

Answer 3

• (s) surface area
• (aq) concentration
• (g) pressure
• 10% of temp

Question 4

what factors affect successfulness?

Answer 4

• 90% of temp
• catalyst

Question 5

rate is proportional to SOLID SURFACE AREA:

Answer 5

• more solid particles are accessible for collisions.
• collision frequency increases.
• successful collision frequency increases.

Question 6

rate is sometimes proportional to SOLUTION CONCENTRATION/ GAS PRESSURE:

Answer 6

• more particles per unit volume.
  -collision frequency increases.
• successful collision frequency increases.

Question 7

rate increases with TEMPERATURE:

Answer 7

• particles have more kinetic energy so particles are faster.
• collision frequency increases.
• larger fraction of collisions have energy greater than activation energy.
• successful collision frequency increases.

Question 8

rate increases in the presences of a CATALYST:

Answer 8

• provides an alternative route with lower activation energy.
• larger fraction of collisions have energy greater than activation energy.
• successful collision frequency increases.

Question 9

what is the distribution of energies in a collection of particles?

Answer 9

Maxwell-boltzmann distributions

Question 10

in graphs that demonstrate Maxwell-boltzmann distributions what is the area under the graph equal to?

Answer 10

the total number of particles.

Question 11

at higher temperatures what happens to the Maxwell-boltzmann distributions graph?

Answer 11

• further right.
• lower.
• drops slower.
• at higher temperature, area under E≥Ea is bigger.

Question 12

what are the two types of catalysts?

Answer 12

homogenenous & heterogeneous

Question 13

what is a homogenous catalyst?

Answer 13

same phase as reacts and products.

Question 14

example of homogenous catalysts?

Answer 14

S₂O₈²-(aq) + 2I-(aq) > 2SO₄²-(aq) + I₂(aq)

step 1: S₂O₈²-(aq) + 2Fe²+ > 2SO₄²- + 2Fe³+

step 2: 2I- + 2Fe³+ > I₂ + 2Fe²+

CATALYST REGENERATED

Question 15

example of heterogeneous catalysts:

Answer 15

“catalytic converters” in cars…
NO(g) + CO(g) > 1/2N₂(g) + CO₂(g)

catalyst: Pt(s) + Rh(s)

NO & CO absorb onto surface so CO bond e- density partially delocalised into metal = weakens bond