enthalpy changes
- Created by: Margaret Hobart
- Created on: 02-05-21 11:13
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- enthalpy changes
- heat energy transferred in a reaction at a constant pressure in kJmol-1
- ?H? means substances were in their standard states and the measurements were made in their standard conditions
- 100KPa and a stated temperature (298 kelvin)
- exothermic: reactions give out energy and have -?H
- making bonds is -?H because energy is released
- if you need less energy to break bonds than is released when bonds are made
- endothermic reactions absorb energy and have +?H
- breaking bonds is +?H because you need energy to break them
- if you need more energy to break bonds than is released when bonds are made
- standard enthalpy of formation ?fH?
- ?H when 1 mol of a compound is formed from its elements in their standard states and under standard conditions
- standard enthalpy of combustion ?cH?
- ?H when 1 mol of a substances completelyburned in oxygen under standard conditions
- standard enthalpy of a reaction ?H?
- enthalpy change when things react together under standard conditions
- the exact energy needed to break the bonds depends on the environment.
- in calculations you use the mean bind enthalpy
- mean bond enthalpy: The enthalpy change when one mole of a type of covalent bond is broken averaged out across the range of compounds
- not exact
- in calculations you use the mean bind enthalpy
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