Enthalpy Change

Question 1

Define enthalpy change in general

Answer 1

The change in heat energy at a constant pressure

Question 2

What are the standard conditions for enthalpy measurements?

Answer 2

Pressure = 100 kPa / 1atmosphere
Temp = 298K / 25 c
Conc = 1 mole dm-3

• reactants and products must be in standard physical states

Question 3

What is the equation for calculating enthalpy change?

Answer 3

Change in enthalpy (KJ) = change in internal energy (KJ) + pressure of system (kPa) x change in volume of system (m3)

Question 4

What process are enthalpy changes of chemical reactions determined by?

Answer 4

Colorimetry

Question 5

There are a few variations of colorimetry but what is common bw all of them?

Answer 5

An experiment is carried out to measure change in temp
- used to calculate Q - energy = mass (g) x constant (4.18) x change in temp

Q = mc delta T

Question 6

Once Q has been calculated, what formula is used to calculate enthalpy change?

Answer 6

Enthalpy change H = Q - energy / mol

Question 7

If the reaction is exothermic and temp goes up, do you put a plus or minus before answer?

Answer 7

Minus, its a neg reaction