3.1.4 - Energetics

Question 1

What is the direction of formation cycle arrows?

Answer 1

Both pointing up

Question 2

Bond breaking is e…

Answer 2

Endothermic

Question 3

Combustion cycle arrows

Answer 3

Both pointing down

Question 4

Bond making is e..

Answer 4

Exothermic

Question 5

Hess’s Law

Answer 5

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

Question 6

What should you remember in calorimetry questions?

Answer 6

The negative sign at the end

Question 7

Define the term standard enthalpy of combustion.

Answer 7

The enthalpy change when one mole of a substance is burnt completely in oxygen under standard conditions

Question 8

What is the definition of mean bond enthalpy? (2)

Answer 8

• The energy required to break one mole of a covalent bond in a molecule
• Averaged over a range of compounds

Question 9

Define the term ‘standard enthalpy of formation’

Answer 9

The enthalpy change when one mole of a substance is formed from its constituent elements with all reactants and products in their standard states.

Question 10

How to get an accurate max temperature reading (4)

Answer 10

1. Start timer when other substance added
2. Record temp every minute for 5 minutes
3. Plot a graph of temperature vs time
4. Extrapolate back to to find the temperature at t=0

Question 11

What is the bond enthalpy equation?

Answer 11

bonds broken (reactants) - bonds formed (products)

Question 12

What do you do if you have Cl2 + F2 - ClF

Answer 12

Divide bond enthalpy of Cl and F by 2, so it is 1/2Cl2 + 1/2F2

Question 13

Define the term enthalpy

Answer 13

Heat energy change at a constant pressure