12) ENTHALPY

Question 1

Name the types of enthalpy

Answer 1

1) Enthalpy of combustion
2) Enthalpy of solution
3) Enthalpy of neutralisation
4) Hesses Law/ Enthalpy of formation
5) Bond Enthalpy

Question 2

Definition of Enthalpy of combustion

Answer 2

The Enthalpy of combustion is the Enthalpy change when 1 mole of a substance is completely burned in oxygen

Question 3

Is Enthalpy of combustion endothermic or exothermic

Answer 3

ALWAYS exothermic

Question 4

What is the formula for working out Enthalpy of combustion

Answer 4

E=cm∆T

C= specific heat capacity (4.18 for water)

M= mass of water (1ml = 1g)

∆T = change in temperature of water

Question 5

What is the definition of Enthalpy of solution

Answer 5

The Enthalpy of solution is the Enthalpy change when 1 mole of substance dissolves in water

Question 6

How would you work out Enthalpy of solution

Answer 6

E=cm∆T

C= specific heat capacity (4.18 for water)

M= mass of water (1ml = 1g)

∆T = change in temperature of water

Question 7

Is Enthalpy is solution endothermic or exothermic

Answer 7

Can be either, look at question to see if there are clues

E.g
There was a rise in temperature = exothermic
Or temperature dropped by = endothermic

Question 8

What do you have to remember about the mass of water when working out Enthalpy while using this formula:

E=cm∆T

Answer 8

Turn the mass of water in kg

Question 9

What are the units when you find out the Enthalpy of one mole

Answer 9

Kg/mole

Question 10

What is Enthalpy of neutralisation

Answer 10

Enthalpy of neutralisation is the Enthalpy change when an acid is neutralised by an alkali to produce 1 mole of water

Question 11

What are the steps in working out Enthalpy of Neutralisation

Answer 11

1) Balance equation
2) work out moles of reactants
3) mole ratio
4) E=cm∆T for water
5) work out energy for 1 mole of water

Question 12

State Hesses Law

Answer 12

The Enthalpy change of a chemical reaction depends only on the chemical nature and physical states of the reactant and products, is independent of any intermediate steps

Question 13

What are the 2 things to look out for when working out Enthalpy of combustion

Answer 13

• look at moles (make sure to balance equation)

* oxygen cannot combust

Question 14

What do the following combust to make:

1) Carbon
2) Hydrogen

Answer 14

1) Carbon dioxide

2) Water

Question 15

What is the final formula for working out Enthalpy of combustion

Answer 15

∆Hx = ∆H1 + ∆H2 - ∆H3

Question 16

Is bond breaking endo or exo

Answer 16

Endothermic. Energy is required

Question 17

Is bond making endo or exo

Answer 17

Exothermic. Energy is realesed

Question 18

What is the formula for working out ∆H is bond Enthalpy

Answer 18

∆H = total bonds broken + total bonds made