U1S4 energetics Flashcards
1
Q
What is enthalpy change
A
- heat energy transferred in a reaction at constant pressure
2
Q
Exothermic reactions
A
- give energy out to surroundings
- temperature increases
- enthalpy change is negative
3
Q
Endothermic reactions
A
- take in energy from surroundings
- temperature falls
- enthalpy change is negative
4
Q
What is bond enthalpy
A
- energy needed to break a bond
5
Q
Calculating enthalpy change
A
- total energy absorbed - total energy released
6
Q
Standard enthalpy change of formation
A
- enthalpy change when 1 mole of a compound is formed from its elements in their standard states under standard conditons
7
Q
Standard enthalpy change of combustion
A
- enthalpy change when 1 mole of a substance is completely burned in oxygen under standard conditions with all reactants and products in their standard states
8
Q
Standard enthalpy change of reaction
A
- enthalpy change when a reaction occurs in the molar quantities shown in the chemical equation, under standard conditions with all reactants and products in their standard states
9
Q
Hess’s law
A
- total enthalpy change for a reaction is independent of route taken
10
Q
How to calculate heat energy change
A
Mass x change in temp x specific heat capacity
11
Q
How to calculate standard enthalpy change
A
Heat energy lost or gained / number of moles
