5) Enthalpy Change Flashcards
Define activation energy
The minimum energy required to start a reaction by breaking bonds
What are the standard conditions
Temp - 298K (25c)
Pressure - 100KPa
Concentration - 1 moldm-3
What are the two most common exothermic reactions
- Combustion of fuels
- Respiration
What are the two most common endothermic reactions
- Thermal decomposition
- Photosynthesis
Define ∆rH
The enthalpy change associated with a stated equation
Define ∆rHθ
The enthalpy change associated with a stated equation in their standard states under standard conditions
Define ∆fH
The enthalpy change when one mole of a compound is made form its elements
Define ∆fHθ
The enthalpy change when one mole of a compound is made from its elements in their standard states under standard conditions
Define ∆cH
The enthalpy change when one mole of a substance is completely combusted with oxygen
Define ∆cHθ
The enthalpy change when one mole of a substance is completely combusted with oxygen under stated conditions
Define ∆neutH
The enthalpy change when an aqueous acid is nuterilised by an aqueous base forming one mole of water
Define ∆neutHθ
The enthalpy change when an aqueous acid is nuterilised by an aqueous base forming one mole of water under standard conditions
What are the steps to calculate enthalpy change from experimental data
1) use Q= -mc∆T
2) Calculate moles of substance burnt
3) use ∆H = Q/n
Where does heat loss occur
- Through the material of the container
- Through the open top of the container
How can we minimise heat loss
- Use an insulating material
- Add a lid
