Unit 1 - Section 4

Question 1

What is enthalpy change?

Answer 1

The heat energy transferred in a reaction at constant pressure and a stated temperature

Question 2

What is bond enthalpy?

Answer 2

The energy required to break a bond

Question 3

What is the standard enthalpy change of formation?

Answer 3

When 1 mole of a compound is formed from elements in there stranded states under stranded conditions

Question 4

What is the standard enthalpy change of combustion?

Answer 4

The enthalpy change when 1 mole of a substance is completely burned in oxygen under standard conditions with all reactants and products in their standard states

Question 5

What is the standard enthalpy change of reaction?

Answer 5

The enthalpy change when a reaction occurs in a molar quantities shown in the equation under standard conditions with all reactants and products in standard state

Question 6

How do you calculate the standard enthalpy change of combustion?

Answer 6

1. Calculate the amount of heat lost or gained during the combustion using q=mc(delta)T
2. Calculate the number of moles of fuel that caused that enthalpy change
3. Use this to calculate the enthalpy change of combustion, using q (found previously) devised by the moles of fuel burnt

Question 7

How do you calculate heat loss or gain?

Answer 7

q = mc(delta)T

q = heat lost or gained
m = mass (in g) of solution being heated
c = specific heat capacity of solution
(Delta)T = temperature change in kelvin

Question 8

What is Hess’s law?

Answer 8

The total enthalpy change for a reaction is independent of the route taken