Energetics Flashcards
Define activation energy:
The minimum amount of energy the reactant particles need in order to collide with each other and react.
What is an exothermic reaction?
A reaction that transfers energy to surroundings, usually in the form of heat.
What is an endothermic reaction?
A reaction that takes energy in from its surroundings.
What is an enthalpy change?
The enthalpy change of a reaction is the heat energy it releases or absorbs per mole.
What is the unit for enthalpy change?
kJ/mol
What does it mean if the enthalpy change has a + sign?
It absorbed heat energy - an endothermic reaction
What does it mean if the enthalpy change has a - sign?
It released heat energy - an endothermic reaction
What happens to the heat energy when bonds break?
They absorb heat energy - endothermic reaction
What happens to the heat energy when bonds are made?
They release heat energy - exothermic reaction
How to calculate ΔH?
ΔH = bonds broken - bonds made
What 2 equations do you need when working out and converting into ΔH in a practical?
Q = m x c x Δt
ΔH = -Q / moles
What is the c in the equations and what is its value?
It’s the specific heat capacity of water.
It is always 4.18 J/g/C
What are the 2 common errors in combustion calorimetry?
- Heat loss - most dissipates into air instead on water
- Incomplete combustion - releases less energy than expected
What substances do you need for combustion calorimetry and how much?
-50g water
-Methanol burner
What substances do you need for solution calorimetry and how much?
-25cm3 CuSO4(aq)
-1g Mg(s)
