Rates of Reactions, Energy Changes and Equilibrium

Question 1

Rate of reaction definition

Answer 1

How quickly a reaction happens

Question 2

Rate of reaction formula

Answer 2

Amount of reactant used or amount of product formed / time

Question 3

Methods of measuring rate of reaction

Answer 3

Precipitation
Change of mass
Volume of gas given off

Question 4

Precipitation method

Answer 4

Works on two see-through solutions that will produce a precipitate
Mix two solutions in a flask over a piece of paper with mark on it
Observe and measure how long mark disappears
Subjective as different people may disagree when mark disappears

Question 5

Change in mass (measuring rate of reaction) method

Answer 5

Works on any reaction that produced a gas
Measure mass of reactants on mass balance
Measure time taken for reaction to finish (when mass balance stops changing)
Measure amount of gas lost and compare with time

Question 6

Volume of gas (measuring rate of reaction) method

Answer 6

Press gas syringe to smallest it can get
Attach it to flask with reactants
More gas given off = faster reaction
Reaction is over when no more gas produced
Have to use right size or else syringe plunger will blow out

Question 7

Factors affecting rate of reaction

Answer 7

Collision frequency (temperature, concentration, surface area)
Energy transferred (temperature, catalyst)

Question 8

Catalyst definition

Answer 8

Substance that increases rate of reaction without being used up

Question 9

Catalyst facts

Answer 9

Provides alternative reaction pathway with lower activation energy
Decreases minimum activation energy
Very fussy with which reactions they can catalyse

Question 10

Enzyme definition

Answer 10

Biological catalysts

Question 11

Exothermic reaction definition

Answer 11

Reaction that gives out more energy to the surroundings than taking in energy, making it warmer

Question 12

Endothermic reaction definition

Answer 12

Reaction that takes in more energy from surroundings than giving energy out, making it cooler

Question 13

Exothermic reaction on reaction profile

Answer 13

Energy in reactants is higher than in products

Difference in height is amount of energy given out

Question 14

Endothermic reaction on reaction profile

Answer 14

Energy in reactants is lower than in products

Difference in height is amount of energy from surroundings absorbed

Question 15

Activation energy definition

Answer 15

Minimum amount of energy needed for bonds to break and a reaction to start
Difference in height between reactants and highest point on curve

Question 16

Measuring temperature change method

Answer 16

Put polystyrene cup into large beaker of cotton wool
Add known volume of first reagent into cup
Measure initial temperature of solution
Add second reaction and stir the reaction mixture
Put lid to reduce energy lost through evaporation
Record maximum or minimum temperature
Calculate temperature

Question 17

Temperature changes in reactions

Answer 17

Dissolving ammonium chloride = endo
Calcium chloride = exo
Most neutralisation = exo
Ethanoic acid + sodium carbonate = endo
Displacement reaction = exo
Precipitation reaction = exo

Question 18

BendoMex

Answer 18

Breaking bonds = endothermic

Making bonds = exothermic

Question 19

Overall energy change formula

Answer 19

Energy required to break bonds - energy released to form bonds

Question 20

Reversible reaction definition

Answer 20

When products of a reaction can react with each other to form the original reactions

Question 21

Haber Process

Answer 21

Process to make ammonia
N2 + 3H2 <==> 2NH3
Carried out at 450°C, 200 atmospheres and iron catalyst

Question 22

How reversible reactions work

Answer 22

As reactants react, their concentration decreases so the rate of forward reaction goes down
The concentration of products then increases so the rate of backward reaction increases
Eventually rate of forward and backward reactions are equal (equilibrium)

Question 23

Things that change position of equilibrium

Answer 23

Temperature
Pressure
Concentration

Question 24

Le Chatelier’s Principle

Answer 24

If there is a change in temperature, pressure or concentration in s reversible reaction, the equilibrium position will change to counteract the change

Question 25

How temperature affects equilibrium position

Answer 25

If temperature decreases, equilibrium will move in exothermic direction to produce more heat
If temperature increases, equilibrium will move in endothermic direction to absorb extra heat

Question 26

How pressure affects equilibrium position

Answer 26

If pressure increases, equilibrium moves towards side with fewer moles of gas to decrease pressure
If pressure decreases, equilibrium moves towards side more more moles of gas to increase pressure

Question 27

How concentration affects equilibrium position

Answer 27

If concentration of reactants increases, equilibrium will move right to use up reactants (more products made)
If concentration of products increases, equilibrium will move to left to use up products (more reactants made)
Decreasing concentration has opposite effect