Chapter 10 Reaction Rates and Equilibrium

Question 1

what is rate of reaction

Answer 1

change in concentration (of reactants or products) in a given amount of time

Question 2

what is the rate of reaction formula

Answer 2

change in concentration / time

Question 3

how does rate of reaction change over time and why

Answer 3

the starts of very fast because there are lots of reactants so the concentration is very high however it gradually gets slower and slower because you begin to run out of the limiting reagent decreasing the concentration of reactants until the rate of reaction is 0 because the reaction has stopped due to their being no more limiting reagent

Question 4

what are the three experimental methods to find rate of reaction

Answer 4

> use a gas syringe and measure how much gas is produced over time
use a cross and see how long it takes for a precipitate to obscure the cross
Use a pH meter to measure acidity of a solution

Question 5

how can you find rate of reaction from a graph

Answer 5

draw a tangent to the graph at t=0 and the gradient of the tangent is the rate of reaction

Question 6

what is collision theory

Answer 6

reactions occur when reactant particles collide with a certain minimum kinetic energy (activation energy)

Question 7

what four factors can increase rate of reaction

Answer 7

> presence of a catalyst
bigger surface area (solid only)
higher temperature
increased concentration/pressure

Question 8

what do squared brackets mean [ … ]

Answer 8

concentration of …

Question 9

what do catalysts do

Answer 9

they are substances that remain chemically unchanged at end of a reaction but speed up rate of reaction by decreasing activation energy

Question 10

how do catalysts decrease the activation energy of a reaction

Answer 10

they provide an alternative reaction pathway for breaking and making bonds with a lower Ea

Question 11

what is a homogeneous catalyst

Answer 11

catalyst that is in the same physical state as the reactants

Question 12

how do homogeneous catalysts work

Answer 12

they react with reactants to form an intermediate which can then break down to form product and regenerates the catalyst

Question 13

why are homogeneous catalysts not normally used in industry

Answer 13

because you then have to process and separate them from the products

Question 14

why are homogeneous catalysts not normally used in industry

Answer 14

because you then have to process and separate them from the products

Question 15

how does a heterogeneous catalyst work

Answer 15

it provides a surface for which a reaction take place

Question 16

what are three steps for how heterogeneous catalyst works

Answer 16

> reactants form weak adsorptive bonds to surface of catalyst
reaction takes place
the products from the reaction desorb off the surface

Question 17

what is the boltzmann distribution

Answer 17

molecules in a sample which are all moving at different speeds/energies

Question 18

what graph is the boltzmann distribution represented on

Answer 18

no of molecules of y axis
energy on x axis
curve that has steep incline then peaks before rapidly decreasing a bit then slowly declining for standard boltzmann distribution
dotted line marking activation energy

Question 19

how do catalysts affect the boltzmann distribution

Answer 19

the catalyst decreases the activation energy required so shifts the activation energy line closer to the start increasing number of molecules with sufficient energy to react when they collide

Question 20

how does increasing temperature affect the boltzmann distribution

Answer 20

increases the number of molecules with sufficient energy so curve increase not as rapidly peaks earlier but then decreases far more gradually

Question 21

what is yield and what is it affected by

Answer 21

how much of a substance is produced

affected by the equilibrium and e Chatelier principle

Question 22

what is rate of reaction affected by

Answer 22

collision theory

Question 23

what is equilibrium

Answer 23

a state of balance where products can be produced and then reverted back into their original reactants

Question 24

what is a dynamic equilibrium

Answer 24

reaction where the forward and backwards reaction continually occur at the same rate within a closed system

Question 25

describe an equilibrium that makes a chemist happy

Answer 25

forward reaction is almost complete when equilibrium is established so the equilibrium favours the products/forward reaction

Question 26

describe an equilibrium that makes a sad chemist

Answer 26

few reactants are converted into products when equilibrium is established so the equilibrium position favours the reactants/reverse reaction

Question 27

what is the concentration rule for equilibriums

Answer 27

whether you start with reactants or products you always get the same concentration values for both

Question 28

what is le Chatelier’s Principle

Answer 28

if a system is in equilibrium and a change is made in any of the conditions then the system responds to counteract the change as much as possible

Question 29

what are three changes that shift an equilibrium

Answer 29

> adding/removing reactants/products
changing pressure
changing temperature

Question 30

how does adding or removing reactants or products shift the equilibrium

Answer 30

adding a substance shifts the equilibrium away from its side

removing a substance shifts the equilibrium towards its side

Question 31

how does changing pressure shift the equilibrium

Answer 31

increasing pressure shifts the equilibrium towards the side with the least moles of gas
decreasing pressure shifts the equilibrium towards the side with the most moles of gas

Question 32

how does changing temperature shift the equilibrium

Answer 32

increasing temperature causes the equilibrium to favour the reaction that is endothermic
decreasing the temperature causes the equilibrium to favour the reaction that is exothermic

Question 33

why do catalysts have no affect on the equilibrium

Answer 33

they remain chemically unchanged and lower the activation energy for both reactions

Question 34

what is Kc

Answer 34

the equilibrium constant that is effectively a ratio of products to reactants

Question 35

what is the general equations for equilibriums

Answer 35

aA + bB ⇌ cC + dD

Question 36

what is the general Kc equation

Answer 36

( [C]^c x [D]^d) / ([A]^a x [B]^b)

Question 37

what do different values for Kc mean

Answer 37

Kc = 1 then equilibrium is in the middle
Kc < 1 equilibrium favours the reactants
Kc > 1 equilibrium favours the products

Question 38

what affects Kc

Answer 38

Amount of substances and pressure have no affect on Kc but changing temperature causes Kc to change