Unit six JT

Question 1

Define standard enthalpy of combustion

Answer 1

The enthalpy change when 1 mole of a substance is burnt in an excess of oxygen under standard conditions

Question 2

Define standard enthalpy of formation

Answer 2

The enthalpy change when 1 mole of a compound (in its standard state) is formed from its constituent elements, under standard conditions

Question 3

Define standard enthalpy of neutralisation

Answer 3

The enthalpy change when an acid and a base react together to form 1 mole of water, with all species in their standard states, under standard conditions

Question 4

What is enthalpy?

Answer 4

The energy/heat content stored in a chemical system

Question 5

What is a chemical system?

Answer 5

The atoms/ions/molecules involved in a chemical reaction

Question 6

Law of conservation of energy

Answer 6

Energy cannot be created nor destroyed

Energy is only transferred between the chemical system and its surroundings

Question 7

ΔfH =

Answer 7

H(products) - H(reactants)

Question 8

What is ΔH for an exothermic reaction?

Answer 8

Negative

Question 9

What is ΔH for an endothermic reaction?

Answer 9

Positive

Question 10

Enthalpy of products and reactants in an exothermic reaction

Answer 10

Enthalpy of products < enthalpy of reactants

Question 11

Enthalpy of products and reactants in an endothermic reaction

Answer 11

Enthalpy of products > enthalpy of reactants

Question 12

What do enthalpy profile diagrams show?

Answer 12

How the enthalpy of the products and reactants changes over time

Question 13

Activation energy definition

Answer 13

The minimum energy required for a reaction to take place

Question 14

Is there an increase or decrease in temperature for an exothermic reaction?

Answer 14

Increase

Question 15

Is there an increase or decrease in temperature for an endothermic reaction?

Answer 15

Decrease

Question 16

q=

Answer 16

mcΔT

Question 17

What does q stand for in q=mcΔT?

Answer 17

Heat exchanged with the surroundings (Joules, J)

Question 18

What does m stand for in q=mcΔT?

Answer 18

Mass of substance heated or cooled (grams, g) (1cm3 = 1g)

Question 19

What does c stand for in q=mcΔT?

Answer 19

Specific heat capacity (4.18Kg-1K-1)

Question 20

What does ΔT stand for in q=mcΔT?

Answer 20

Change in temperature (k)`

Question 21

Specific heat capacity definition

Answer 21

The amount of energy (heat) required to increase the temperature of one gram of a substance by 1k (1C)

Question 22

Specific heat capacity of water

Answer 22

4.18Jg-1K-1

Question 23

How to use q=mcΔT to calculate ΔH

Answer 23

1. q = mcΔT
2. n of solid = mass / Mr
   3) Energy per mole = q / n
   4) Add + or - to represent temperature fall or rise

Question 24

Zn(s) + CuSO4(aq) –>

Answer 24

ZnSO2(aq) + Cu(s)

Question 25

Zinc + Copper sulfate –>

Answer 25

Zinc sulfate + Copper

Question 26

Gallium sulfate

Answer 26

Ga2(SO4)3

Question 27

Magnesium phosphate

Answer 27

Mg3(PO4)2

Question 28

Aluminium sulfide

Answer 28

Al2S3

Question 29

Bond enthalpy definition

Answer 29

Bon enthalpy is the energy change when breaking (by homolytic fission) one mole of a given bond in the molecules of a gaseous species

Question 30

Bond formation is

Answer 30

Exothermic

Question 31

Bond breaking is

Answer 31

Endothermic

Question 32

% error =

Answer 32

[(error x number of readings) / (value)] x 100

Question 33

A catalyst lowers

Answer 33

Activation energy

Question 34

Standard pressure

Answer 34

289K

Question 35

Standard pressure

Answer 35

100kPa

Question 36

ΔcH=

Answer 36

H(reactants) - H(products)