Chemistry Module 4

Question 1

What is thermodynamics?

Answer 1

Thermodynamics is the study of the relations between heat, work, temperature, and energy.

Question 2

What is the enthalpy change?

Answer 2

It is the heat energy change of a reaction held at a constant pressure. This means how much energy is released or absorbed in a reaction.
- the amount of energy the products have compared to the reactants

Question 3

What is the symbol for Enthalpy change?

Answer 3

ΔH - Delta H
Δ = change in
H= enthalpy

Question 4

What unit is used for enthalpy change.

Answer 4

It is Joules, the standard unit for energy.
Or kilojoules if large amounts of energy are released or absorbed.

Question 5

Why are enthalpy reactions often shown as kilojoules per mole?

Answer 5

• it factors the amount of substance we have
• for eg. the reaction of a small lab experiment will be different to a chemical reaction of the same product during industrial production
• often give enthalpy change for each mole of substance reacting

Question 6

Note of enthalpy

Answer 6

• the reaction gives out energy - delta h is negative
• reactant energy is greater than product energy
• if the reaction absorbs energy from the surroundings, the enthalpy change is positive

Question 7

What are the standard conditions for measuring enthalpy change?

Answer 7

• specific temperature and pressure
• temp: 25 degrees celsius (298K)
• pressure: 100 kPa

Question 8

What symbol is added to the enthalpy when the reaction is under standard conditions?

Answer 8

the circle with the horizontal line in it

Question 9

How would standard condition in enthalpy change apply?

Answer 9

All reactions must be in their original/usual physical states.