Reactivity 1.2

Question 1

What sort of process is bond breaking?

Answer 1

Endothermic

Question 2

What sort of process is bond forming?

Answer 2

Exothermic

Question 3

In terms of bond breaking and forming, describe when a reaction would be exothermic.

Answer 3

The energy released from forming new bonds is greater than the energy needed to break existing bonds

Question 4

In terms of bond breaking and forming, describe when a reaction would be endothermic.

Answer 4

The energy needed to break existing bonds is greater than the energy released from forming new bonds

Question 5

To use average bond enthalpies to determine an enthalpy change of reaction, which state must all reactants and products be

Answer 5

Gas

Question 6

Describe how to calculate the enthalpy of reaction using bond enthalpy values

Answer 6

The sum of the energies needed to break bonds in the reactants minus the energy released when the new bond are formed in the products

Question 7

Define bond enthalpy

Answer 7

The enthalpy change needed to break one mole of bonds in a gaseous molecule averaged over similar compounds

Question 8

Explain why experimentally determined enthalpy of reaction values are always different from theoretical enthalpy of reaction values calculated using bond enthalpy data

Answer 8

Bond enthalpy values in the data booklet are averages of that bond in many different molecules, whilst the experimental data will be determined using a specific molecules.

Question 9

Explain why the bond enthalpy values in the data booklet are averages

Answer 9

They are an average value of the bond enthalpy for the same bond in different environments or molecules

Question 10

Determine the enthalpy required to break all the bonds in 1.00 mol of nitrogen molecules

Answer 10

(+) 945 kJ mol⁻

Question 11

Determine the enthalpy released when forming all the bonds in 1.00 mol of nitrogen molecules

Answer 11

(-) 945 kJ mol⁻

Question 12

Determine the enthalpy required to break all the bonds in 1.00 mol of oxygen molecules

Answer 12

(+) 498 kJ mol⁻

Question 13

Determine the enthalpy released when forming all the bonds in 1.00 mol of oxygen molecules

Answer 13

(-) 498 kJ mol⁻

Question 14

Determine the enthalpy required to break all the bonds in 1.00 mol of carbon dioxide molecules

Answer 14

(+) 1608 kJ mol⁻

Question 15

Determine the enthalpy released when forming all the bonds in 1.00 mol of carbon dioxide molecules

Answer 15

(-) 1608 kJ mol⁻

Question 16

Determine the enthalpy required to break all the bonds in 1.00 mol of methane molecules

Answer 16

(+) 1656 kJ mol⁻

Question 17

Determine the enthalpy released when forming all the bonds in 1.00 mol of methane molecules

Answer 17

(-) 1656 kJ mol⁻

Question 18

Determine the enthalpy required to break all the bonds in 1.00 mol of propene molecules

Answer 18

(+) 3444 kJ mol⁻

Question 19

Determine the enthalpy released when forming all the bonds in 1.00 mol of propene molecules

Answer 19

(-) 3444 kJ mol⁻

Question 20

Using section 12 of the data booklet, determine the total enthalpy required to break all the bonds in the following reactants

Answer 20

(+) 1898 kJ mol⁻

Question 21

Using section 12 of the data booklet, determine the total enthalpy required to break all the bonds in the following reactants

Answer 21

(+) 2582 kJ mol⁻

Question 22

Using section 12 of the data booklet, determine the total enthalpy required to break all the bonds in the following reactants

Answer 22

(+) 6494 kJ mol⁻

Question 23

Using section 12 of the data booklet, determine the total enthalpy released to form all of the bonds in the following products

Answer 23

(-) 1997 kJ mol⁻

Question 24

Using section 12 of the data booklet, determine the total enthalpy released to form all of the bonds in the following products

Answer 24

(-) 2385 kJ mol⁻

Question 25

Using section 12 of the data booklet, determine the total enthalpy released to form all of the bonds in the following products

Answer 25

(-) 8528 kJ mol⁻

Question 26

Using section 12 of the data booklet, calculate the overall enthalpy change of the following chemical reaction

Answer 26

- 99 kJ mol⁻ - MUST INCLUDE THE NEGATIVE SIGN

Question 27

Using section 12 of the data booklet, calculate the overall enthalpy change of the following chemical reaction

Answer 27

(+) 197 kJ mol⁻ - MUST INCLUDE THE POSITIVE SIGN

Question 28

Using section 12 of the data booklet, calculate the overall enthalpy change of the following chemical reaction

Answer 28

- 2034 kJ mol⁻ - MUST INCLUDE THE NEGATIVE SIGN

Question 29

A forward reaction has an enthalpy change of +244 kJ mol⁻, what is the enthalpy change for the reverse reaction?

Answer 29

-244 kJ mol⁻ - MUST INCLUDE THE NEGATIVE SIGN

Question 30

What is the first thing you should do when calculating the total bond enthalpy for a molecule

Answer 30

Draw out the molecule including all of the bonds

Question 31

If a substance in a chemical reaction has a coefficient greater than 1, how would you calculate the total bond enthalpy for the substance

Answer 31

Total bond enthalpy for one molecule of the substance multiplied by the coefficient

Question 32

When counting the bonds in a molecule, how can you ensure you do not forget to count a bond

Answer 32

Tick off each bond on the molecule drawing once it has been counted

Question 33

Describe the relationship between bond enthalpy and bond length

Answer 33

The shorter the bond length, the higher the bond enthalpy

Question 34

Describe the relationship between bond enthalpy and bond polarity

Answer 34

The higher the bond polarity, the higher the bond enthalpy

Question 35

Define Hess's Law

Answer 35

The overall enthalpy change for a chemical reaction is the same independent of the route taken as long as the initial and final conditions are the same.

Question 36

Construct an equation to use Hess's law to determine ΔH

Answer 36

ΔH = ΔH1 + ΔH2 + ΔH3

Question 37

Construct an equation to use Hess's law to determine ΔH1

Answer 37

ΔH1 = AH - ΔH3 - ΔH2

Question 38

Construct an equation to use Hess's law to determine ΔH2

Answer 38

ΔH2 = -ΔH1 + ΔH - ΔH3

Question 39

Construct an equation to use Hess's law to determine ΔH3

Answer 39

ΔH3 = -ΔH2 -ΔH1 + ΔH

Question 40

Construct an equation to use Hess's law to determine ΔH2

Answer 40

ΔH2 = ΔH1 - ΔH3

Question 41

Construct an equation to use Hess's law to determine ΔH5

Answer 41

ΔH5 = -ΔH4 + ΔH1 - ΔH6

Question 42

When using Hess's law describe what you must do to the enthalpy change if you are moving in the opposite direction to the reaction arrow

Answer 42

Change the sign OR Change from + to - and vice versa

Question 43

Define the standard enthalpy of formation

Answer 43

The enthalpy change when 1 mole of a substance is formed from its constituent elements in the standard states under standard conditions

Question 44

State the standard enthalpy of formation for any element

Answer 44

0

Question 45

State the standard enthalpy of formation for hydrogen gas

Answer 45

0

Question 46

Describe how to use standard enthalpy of formation data to calculate the standard enthalpy of reaction

Answer 46

The sum of the standard enthalpies of formation of the products minus the sum of the standard enthalpies of formation of the reactants.

Question 47

Construct a balanced symbol equation to represent the standard enthalpy of formation of 1.00 of water

Answer 47

H₂ (g) + 1/2O₂ (g) --> H₂O (l)

Question 48

Construct a balanced symbol equation to represent the standard enthalpy of formation of 1.00 of benzene

Answer 48

3H₂ (g) + 6C (s) --> C₆H₆ (l)

Question 49

Construct a balanced symbol equation to represent the standard enthalpy of formation of 1.00 of ethanol

Answer 49

2C (s) + 1/2O₂ (g) + 3H₂ (g) --> C₂H₅OH (l)

Question 50

When constructing a balanced symbol equation to represent the standard enthalpy of formation, what should the coefficient of the product be?

Answer 50

1

Question 51

When constructing a balanced symbol equation to represent the standard enthalpy of formation, how should you represent 1 H atom as a reactant?

Answer 51

1/2 H₂ or 0.5H₂