8 Enegetics

Question 1

What are the two types of energy change that can occur?

Answer 1

• endothermic (absorb heat from surroundings)
• exothermic (release heat to surroundings)

Question 2

Equation of energy transfer?

Answer 2

Q = mcΔT

Q - energy transfer (J)
m - mass of solution (g)
c - SHC of water (4.18 J/gK)
ΔT - temperature change (K)

Question 3

Equation of enthalpy change?

Answer 3

ΔH = Q/n

ΔH = enthalpy change (kJ/mol)
Q = energy transfer (J)
n = moles of limiting reactant

Question 4

Define “standard enthalpy of combustion”

Answer 4

Heat energy released when 1 mole of a substance is burnt completely in oxygen under standard conditions

Question 5

Define “enthalpy of neutralisation”

Answer 5

The energy change when 1 mole of water is formed in a reaction between an acid and a base

Question 6

Define “enthalpy of formation”

Answer 6

The energy change when 1 mole of a substance is formed from their elements in their standard state under standard conditions

Question 7

What does Hess’ Law state?

Answer 7

The energy change for a chemical reaction is always the same regardless of the route taken

Question 8

Define “bond energy”

Answer 8

Energy required to break the covalent bond for 1 mole of a substance

Question 9

Why could calculations using mean bond enthalpy be inaccurate?

Answer 9

• substances not in gases state
• actual bond enthalpies can vary