Enthalpy change - DF

Question 1

Enthalpy change shown as

Answer 1

ΔH

Question 2

What does change in enthalpy mean

Answer 2

change in enthalpy is referred to the amount of heat lost or taken in from the surroundings, when a reaction occurs

Question 3

Enthalpy level diagrams (exothermic)

Answer 3

ΔH is negative, energy is given out to surroundings (gets hotter)
https://s3.eu-west-2.amazonaws.com/elements.cognitoedu.org/7d33a897-872d-43d8-bbbd-3950a11f8578/enthalpy-profile-diagrams.png

Question 4

Enthalpy level diagrams (endothermic)

Answer 4

ΔH is positive, energy is taken in from surroundings (gets cooler)
https://s3.eu-west-2.amazonaws.com/elements.cognitoedu.org/7d33a897-872d-43d8-bbbd-3950a11f8578/enthalpy-profile-diagrams.png

Question 5

Units of ΔH
Units of temperature (and conversion)

Answer 5

kJ/mol
Kelvin (K)
Celsius —–+273—-> Kelvin

Question 6

Standard conditions of enthalpy change

Answer 6

temperature = 25°C
pressure = 1 atm
concentration of solutions = 1mol/dm^3
substances are in their standard states = the state of that substance under standard conditions

Question 7

How to show that enthalpy change is in standard conditions

Answer 7

ΔH^θ

Question 8

Why is enthalpy change done in standard conditions

Answer 8

as ΔH vary with temperature, pressure, concentration etc. so to compare values they need to be in a standard condition