Topic 5.1 - Measuring energy changes Flashcards
1
Q
Working out ΔH
A
Use q = mcΔT
Use ΔH - q/n
2
Q
q = mcΔT
A
q = heat in J m = mass of solution (water normally) in g (1g = 1cm³) c = SHC of water (assumption: solution = water) in J/K⁻¹/g⁻¹ ΔT = temperature change in K or °C
3
Q
ΔH = q/n
A
ΔH = enthalpy change in kJ mol⁻¹ q = heat energy in J n = number of moles (use mass and Mr of main focus)
4
Q
Systematic errors
A
Cause a percentage error.
Caused by:
- heat loss to surroundings
- not all heat transferred to solution (water)
- incomplete combustion
5
Q
Enthalpy of formation
A
Enthalpy change that occurs upon the formation of one mole of gaseous ions from its elements under standard conditions
6
Q
Enthalpy of combustion
A
Enthalpy change that occurs when one mole of a molecule is burnt in excess oxygen
7
Q
Bond breaking
A
Energy is taken in to break the bonds: enthalpy change is + and the reaction is endothermic
8
Q
Bond forming
A
Energy is released when the bonds are formed: enthalpy change is - and the reaction is exothermic
