Ch11 Rates and equilibria

Question 1

Collision theory

Answer 1

a reaction cannot take place unless a successful collision takes place between reacting particles

Question 2

successful collision

Answer 2

1. Colliding particles are correctly orientated(opposite charges)
2. The energy of the collision must exceed the activation energy of that particular reaction

Question 3

4 ways the frequency of collisions can be increased

Answer 3

1. increasing concentration
2. increasing surface area of a solid
3. increasing temperature
4. increasing pressure in gaseous reaction

Question 4

Effect of concentration/pressure

Answer 4

Increases chance of collision as there are same amount of particles in smaller volume
- more collisions, faster reaction

Question 5

Effect of surface area

Answer 5

More surface is exposed to reagent so more collisions occur

Question 6

Effect of temperature

Answer 6

Increases the energy of particles and so increases the number of particles over activation energy(boltzmann distribution)

Move faster and more randomly so more successful collisions

Question 7

Effect of a catalyst

Answer 7

Provide an alternative route or mechanism for the reaction that has a different activation energy without getting used up

Question 8

Homogenous catalyst

Answer 8

Same phase as reaction mixture

Question 9

Heterogenous catalyst

Answer 9

• different phase from reactants
• adsorbs gases onto solid catalyst surface
• adsorption weakens bonds within reactant molecules
• bonds are broken and new bonds are formed
• product molecules are then desorbed from surface

Question 10

Example homogenous catalyst

Answer 10

S2O8^2- + 2I- -> 2SO4^2- + I2

1. 2O8^2- + 2Fe^2+ - -> 2SO4^2- + I2

Question 11

Example of heterogenous catalysts

Answer 11

N2(g) + 3H2(g) <=Fe=> 2NH3(g)

Question 12

economic importance of catalysts

Answer 12

• reduction in energy requirements means less temperatures so lower costs
• reduces demands of fossil fuels
• reduces pollution

Question 13

Dynamic equilibrium

Answer 13

• The rate of the forwards reaction equals the rate of the backwards reaction
• The concentration of reagents and products remain constant
• Products and reactants react continuously

Question 14

Le Chateliers principle

Answer 14

If a closed system at equilibrium is subject to change, the system will move to minimise the effect of that change

Question 15

Effect of increasing pressure on dynamic equilibrium

Answer 15

system will move to the side with
fewer moles in order to decrease the pressure

Question 16

Effect of increasing temperature on dynamic equilibrium

Answer 16

system will move in the
endothermic direction in order to decrease the temperature

Question 17

Effect of catalyst on equilibrium

Answer 17

Catalysts speeds up forward and reverse reaction equally, so equilibrium position stays the same

Question 18

effect of increasing concentration on equilibrium

Answer 18

system will move to remove that substance

Question 19

Haber process

Answer 19

N2(g) + 3H2(g) <=> 2NH3(g)

Forward reaction is exothermic

Question 20

Manufacturing conditions of haber process

Answer 20

700k
200 atmospheres
catalyst of porous iron

Question 21

Equilibrium constant

Answer 21

Kc = [C]^c [D]^d / [A]^a [B]^b