Energetics Flashcards
1
Q
define enthalpy change
A
the heat change at constant pressure
2
Q
define Standard enthalpy of formation
A
- the enthalpy change when 1 mol of a substance is formed from its elements under standard conditions with all substances in standard states
2
Q
what are the standard conditions needed for standard enthalpy change
A
- 298K
- 100kPa
3
Q
define Standard enthalpy of combustion
A
- the enthalpy change when 1 mol of a substance is completely burned in oxygen under standard conditions with all substances in standard states
4
Q
what is the enthalpy of formation of an element
A
- zero by definition
4
Q
what does a hess cycle look like when using enthalpy of formation data and what is the equation used?
A
- elements in their standard state at bottom
- the arrows point upwards
- Δ H Formation = ( Δ H f ) Products − ( Δ H f ) Reactants
5
Q
what does a hess cycle look like when using enthalpy of combustion data and what is the equation used?
A
- products at the bottom
- the arrows point downwards
- Δ H Combustion = ( Δ H f ) Reactant − ( Δ H f ) Products
6
Q
define Bond Dissociation Energy
A
- enthalpy change to break the bond in 1 mol of gaseous molecules to form gaseous atoms
7
Q
what are equation links heat energy with specific heat capacity
A
- q = mc∆t
q = heat energy (joules)
m = mass (grams)
c = specific heat capacity (4.18 JK⁻¹g⁻¹
∆t = change in temp
7
Q
A
7
Q
what are equation links heat energy with enthalpy change
A
- ΔH = q/n
q = heat energy (kilojoules)
n = number of moles
7
Q
A
8
Q
what equation links bond enthalpy with enthalpy change
A
ΔH = Σ bond energies broken - Σ bond energies made
8
Q
A
