Chemistry A-Level
sign of ∆H
What sign of ∆H means in Chemistry A-Level, as defined for AQA, OCR.
Definitions of sign of ∆H
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Reference: OCR
ΔH is positive for an endothermic reaction and negative for an exothermic reaction, linked to the net balance of bond breaking and bond making.
The sign records the balance: negative when the system loses energy to the surroundings, positive when energy is drawn from the surroundings.
Topics that use sign of ∆H
- Enthalpy change (AQA A-Level)
- Enthalpy changes (OCR A-Level)
Related terms
- enthalpy change
- ∆H of combustion
- ∆H of formation
- Activation energy
- Approximate estimate
- Average bond enthalpy
- Averaging over gaseous compounds
- Bond breaking and bond making
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