Module 3.2

Question 1

Enthalpy change equation

Answer 1

Products - reactants

Question 2

Exothermic reaction

Answer 2

Heat energy is released from the chemical system

- the enthalpy of the product is smaller than the reactant

Question 3

Endothermic reaction

Answer 3

Chemical system has taken in energy from the surroundings so temperature of the surroundings has decreased
- enthalpy of the product is greater than the reactant

Question 4

Standard enthalpy change of combustion

Answer 4

The enthalpy change when one mole of a substance reacts completely with oxygen under standard conditions

Question 5

Standard enthalpy change of neutralisation

Answer 5

The enthalpy change when one mole of water is formed in a neutralisation reaction under standard conditions

Question 6

Why is the standard enthalpy change of neutralisation the same in any strong acid and strong alkali ?

Answer 6

• because the key parts of the reaction a H+ in the acid and the OH- on the alkali which are the same

Question 7

Standard enthalpy change of formation

Answer 7

the enthalpy change when one mole of a compound is formed from its element under standard conditions

Question 8

Standard enthalpy change of a reaction

Answer 8

Enthalpy change associated with a stated equation

Question 9

Activation energy

Answer 9

The minimum energy required for a reaction to take place

Question 10

standard states and conditions of enthalpy change

Answer 10

• pressure=100kpa
• Temperature=298 k (25degrees)
• concentration= 1 mol dm3

Question 11

enthalpy change from calorimetry equation

Answer 11

• q= m x c x temp change

Question 12

how to calculate enthalpy change of combustion

Answer 12

q = m x temp change x temp change (k)

- divide by moles of fuel used

Question 13

why is the experimental value lower than the actual enthalpy change?

Answer 13

• Heat loss to surroundings (use a lid and polystyrene cup over glass to prevent this)
• Heat is absorbed by the container
• incomplete combustion
• evaporation

Question 14

what is the advantage of using a bomb calorimeter?

Answer 14

• minimises heat lost, uses pure oxygen to ensure complete combustion is achieved therefore the experimental value is more accurate.

Question 15

how to calculate enthalpy change of neutralisation

Answer 15

• q= m x c x temp change
• workout more of water produced by finding the moles of the reactant and using balanced mole equation to find moles of water produced.
• energy/ moles
• add - if its exothermic

Question 16

average bond enthalpy

Answer 16

• the energy needed to break one mole of a specific bond in a molecule in the gaseous state

Question 17

how do we calculate bond enthalpy

Answer 17

• write a chemical equation using display formulae
• tally number of bond in reactants and products and substitute
• reactants - products

Question 18

Hess law

Answer 18

• enthalpy change in a chemical reaction is independent of the route it takes.

Question 19

Hess cycle to calculate enthalpy change

Answer 19

• write out all the elements involved in the reaction. if combustion co2 and h20
• fill in the enthalpy data
• change the sign . right if formation left if combustion
• add enthalpy change of reactant and product

Question 20

Collison theory

Answer 20

• for a reaction to occur the particles must collide in the right direction and have the minimum anount of kinetic energy

Question 21

Formulae for rate of reaction

Answer 21

Amount of reactant used/product made/ time

Question 22

Effect of concentration on the rate of reaction

Answer 22

• increased concentration= increase rate of reaction
• the molecules are closer together so there is a greater chance of them colliding with sufficient energy to overcome the activation energy
• more successful collisions

Question 23

Effect of pressure on the rate of reaction

Answer 23

• pressure of gas increases= rate of reaction increases
• same number of molecules occupies a smaller volume
• more successful collisions

Question 24

Effect of temperature on the rate of reaction

Answer 24

• increase temperature = increased rate of reaction
• increases kinetic energy and move faster
• higher proportion of molecules have an energy that is greater than the active energy
• more successful collisions

Question 25

Effect of catalyst on the rate of reaction

Answer 25

- more particles hace enough energy to reach the activation barriar - more successful collisons = rate of reaction increases

Question 26

Catalyst

Answer 26

Substances that increased the rate of reaction by providing an alternative pathway that lowers activation energy . The catalyst is chemically by the end of the reaction

Question 27

Hetergeneous catalyst

Answer 27

- a catalyst that is a different phase from the reactant. E.g. solid catalyst used in liquid reactants increasing the SA of this increases rate of reactions as more particles can react with the catalyst at the same time.

Question 28

homogeneous catalyst

Answer 28

- catalyst that is in the same phase as the reactant. generally AQ and AQ. they are used up in a reaction forming an intermediate species from the reactant combining which reacts to form a product, the catalyst is remformed again

Question 29

benefits of using a catalyst

Answer 29

- reduces energy demand resulting in reduction in co2 emissions and lowering cost - catalytic converters reduces toxic emission from vehicles preventing photochemical smog by converting toxic carbon monoxide and nitrogen oxide into co2 and n2, - improves stainability

Question 30

which ways can we measure the rate of reaction

Answer 30

- measure how long it takes preticipate to form - volume of gas produced using a gas syringe - mass lost

Question 31

Dynamic equilibrium

Answer 31

Equilibrium exist in a closed system when the rate of the foward reaction is equal to the rate of the reverse reaction and the concentration of reactants and products do not change

Question 32

Effect of catalyst on equilibriums

Answer 32

- speeds up the rate in which a reaction reaches a equilibrium - increases the rate of both foward and reverse reactions by the same amount resulting in a unchanged position of equilibrium

Question 33

What is meant when kc value is greater than 1

Answer 33

- the reaction favours the products

Question 34

Kc is smaller than 1

Answer 34

- the reactant favours the products

Question 35

Kc=

Answer 35

Products/ reactants