Enthalpy Flashcards
1
Q
What is the equation for enthalpy?
A
ΔH = cmΔT change in chemical energy = specific heat capacity x mass x change in tempurature
2
Q
What is the unit of enthalpy?
A
kJ or kJ mol-1
3
Q
What is the definition of activation energy?
A
the minimum energy needed by colliding reactants for a reaction to occur
4
Q
What is enthalpy change?
A
the change in potential energy when products are formed from reactants
5
Q
What is an exothermic reaction
A
- It is where the energy change is negative (∆H > 0 kJ mol-1)
- It is a reaction where energy is released
- Heat energy is given out to the surroundings as the total energy of the bonds broken is less than the bonds formed
- an example is burning fuels (2C2H6 + 7O2 -> 4CO2 + 6H2O), condensation, freezing
6
Q
What is an endothermic reaction?
A
- The enthalpy change is positive (∆H > 0 kJ mol-1)
- Heat energy is taken in from the surroundings: temperature falls as the total energy of the bonds broken is more than the bonds formed
- an example is e.g. photosynthesis (6H2O + 6CO2 -> C6H12O6 + 6O2), melting, evaporation, dissolving salts (e.g. Ammonium nitrate)
7
Q
What is the equation for the enthalpy of the reaction of gases?
A
∆H = sum of all the reactants’ bond energies - sum of all the products’ bond energies
8
Q
A
