5.2 ENERGETICS Flashcards
Define an enthalpy change of a reaction
The heat energy it releases or absorbs per mole
Is heat energy absorbed or released in an ENDOthermic reaction (and so what enthalphy sign is it)
Absorbed (+)
Is heat energy absorbed or released in an EXOthermic reaction (and so what enthalphy sign is it)
Released (-)
Units of enthalpy
kJ/mol
How do you draw an energy level diagram for an ENDOthermic reaction
- Enthalpy scale on y-axis, and time/progression on x-axis
- Reactants drawn on line on bottom of diagram
- Vertical line up with an arrow (labelled with enthalpy)
- Products of horizontal line above line
How do you draw an energy level diagram for an EXOthermic reaction
- Enthalpy scale on y-axis, and time/progression on x-axis
- Reactants drawn on line at top of diagram
- Vertical line down with an arrow (labelled with enthalpy)
- Products of horizontal line below
When bonds are broken, what type of reaction is it
Endothermic - energy is absorbed
When bonds are made, what type of reaction is it
Exothermic - energy is released
Unit for bond energy
kJ/mol
Equation for calculating with bond energies
Enthalpy change = Bonds broken - bonds made
How to calculate a bond energy question
- Add up each individual bond energy for each bond
- Add them together for products and reactants
- Subtract products from reactants
In an exothermic reaction, what is the ‘ratio’ of energy absorbed / released
Released > Absorbed
In an endothermic reaction, what is the ‘ratio’ of energy absorbed/released
Absorbed > Released
In an endothermic reaction, what is the ‘ratio’ of energy absorbed/released
Absorbed > Released
What is the activation energy
The energy needed to break the bonds