energetics 3.1.4 in all papers Flashcards
1
Q
enthalpy change
what is an enthalpy change?
A
- the heat energy change measured under constant pressure.
- its measured in J/KJ per moles.
2
Q
enthalpy change
what does standard enthalpy change refer to?
A
- standard conditions, 100kpa, 25 degrees/ 298 kelvins.
3
Q
enthalpy change
what is an endothermic reaction?
A
- a reaction where heat energy is transferred from the surrondings to the reactants, tempreture decreases.
3
Q
enthalpy change
what is an exothermic reaction?
A
- a reaction where heat energy is released to the surrondings.
4
Q
enthalpy change
what is bond breaking?
A
- the input of energy, making it endothermic (+).
5
Q
enthalpy change
how do you work out enthalpy change?
A
- mass of water (g) x change in tempreture of water x specific heat capacity of water (KJ).
- assuming that all energy from the burning fuel is transferred to the water.
- density g of water is 1gcm-3, so 24.5cm3 g of water = 24.5 g
6
Q
enthalpy change
what is bond making?
A
- the output of energy, making it exothermic (-).
7
Q
enthalpy change
what is standard enthalpy of combustion?
A
- the enthalpy change when 1 mole of a substance is completely burnt in excess oxygen with all reactants being in their standard state under standard conditions.
8
Q
bond enthalpy
define mean bond enthalpy.
A
- the energy required to break 1 mole of a covalent bond averaged across many compounds containing the bond.
9
Q
bond enthalpy
which type of bonds are stronger?
A
- shorter the covalent bond, the stronger the bond.
- triple bonds are generally shorter than double or single bonds, so more energy is required to break them resulting in a positive bond enthalpy.
