1.4 Energetics Flashcards
What happens to energy when bonds are broken and formed
Bonds broken = energy taken in from surroundings
Bonds formed = energy is given out
What are the standard conditions for measuring enthalpy
- 100 kPA pressure
- 298 K temperature
Define Standard Enthalpy of Formation
The enthalpy change when one mole of a compound is formed from its elements in their standard states under standard conditions
Define enthalpy change
Enthalpy change is the heat energy change at constant pressure
Define Standard Enthalpy of Combustion
The enthalpy change that occurs when one mole of a substance undergoes complete combustion in excess oxygen under standard conditions
What is the enthalpy change of Endothermic reactions
(-ve / +ve)
Positive enthalpy change
(energy taken in)
What is the enthalpy change of Exothermic reactions
(-ve / +ve)
Negative enthalpy change
(energy is released)
How to calculate enthalpy change
Enthalpy change = bond broken - bonds formed
Define specific heat capacity
Energy required to raise 1g of a substance, by 1K, without a change of state
What is Hess’ Law
Energy in a reaction system must be conserved, so it doesnt matter which route it takes
Which direction do the arrows point during enthalpy formation
Arrows point out from central product
Which direction do the arrows point during enthalpy combustion
Towards the central product (which is always H2O and CO2)
