Enthalpy Changes

Question 1

Define enthalpy change

Answer 1

Enthalpy change (delta H), is the heat energy transferred in a reaction at constant pressure.

Question 2

What are standard conditions of enthalpy change?

Answer 2

Standard conditions are 100kPa pressure and a stated temperature

Question 3

What does exothermic mean?

Answer 3

Exothermic reactions give out energy. Delta H is negative

Question 4

What does endothermic mean?

Answer 4

Endothermic reactions absorb energy. Delta H is positive

Question 5

Is bond breaking endothermic or exothermic?

Answer 5

You need energy to break bonds,so bond breaking is endothermic. Stronger bonds take more energy to break

Question 6

Is bond making endothermic or exothermic?

Answer 6

Energy is released when bonds are formed, so bond making is exothermic. Stronger bonds release more energy when they form

Question 7

What is bond enthalpy?

Answer 7

Bond enthalpy is the energy required to break bonds

Question 8

Does breaking the same bond require the same amount of energy

Answer 8

The same types of bond don’t always require the same amount of energy to break, the energy needed to break the bond depends on the environment it’s in

Question 9

Define mean bond enthalpy

Answer 9

Mean bond enthalpy is the average energy needed to break a certain type of bond, over a range of compounds

Question 10

Define standard enthalpy of formation

Answer 10

Standard enthalpy of formation is the enthalpy change when 1 mole of a compound is formed from its elements in their standard states and under standard conditions

Question 11

Define standard enthalpy of combustion

Answer 11

Standard enthalpy of combustion is the enthalpy change when 1 mole of a substance is completely burned in oxygen under standard conditions