Zusammenfassung der Ressource
OCR - A-Level -
Chemistry -
Enthalpy Changes
- Enthalpy is the amount
of thermal energy stored
by chemicals in a system.
- Represented
as H
- ΔH, +ve means it
is endothermic
- +ve because
gaining energy
- In endothermic reactions,
products have more energy
than reactants. Energy taken
in from the surroundings.
- ΔH, -ve means it
is exothermic
- -ve because
losing energy
- In exothermic reactions,
products have less energy
than reactants. Energy given
out to the surroundings.
- With a catalyst,
activation energy
needed is reduced.
- Exothermic
- Endothermic
- A system is
the reactants
and products.
- Standard conditions
- 100kPa
- 298K (25
degrees Celsius)
- 1.0M concentration
- Standard state is the
most stable physical state
of a substance under
standard conditions
- Magnesium is Mg(s)
- Hydrogen is H2(g)
- Water is H2O(l)
- Enthalpy
change of
reaction
- Balanced
chemical
equation
- Enthalpy
change of
formation
- Only 1 mole
of the product
- Enthalpy
change of
combustion
- Only 1 mole of the
fuel substance
- Enthalpy
change of
neutralisation
- Only 1 mole
of water