Energetics

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Energetics
Thermodynamics
1st rules of thermodynamics/ law of conservation of energy energy can be neither
created or destroyed
E=mc2 Energy = mass x speed of light2
Heat is a form of kinetic energy causes the random movement of atoms and molecules
to increase
Temperature is the average energy of the random motion of the atoms and molecules
Heat is measured in joules (J) or kilojoules (kJ) 1kJ = 1000J
Q=mc^T heat required = mass x specific heat capacity x temperature change
Temperature measured in degrees C or Kelvin
Enthalpy change
The change in enthalpy that takes place during a reaction ^H = Hproducts - Hreactants
Enthalpy the chemical energy in the system at constant pressure that can be converted
to heat
System the reaction mixture
Surroundings everything outside the system
Exothermic reactions that produce heat energy (-ive ^H)
Endothermic reactions that take in heat energy (+ive ^H)
Enthalpy of a substance depends on:

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The physical state of the substance
o The amount in moles of the substance
o The temperature and pressure
Standard enthalpy change enthalpy change under standard conditions:
o 1 atm pressure
o Stated temperature (usually 25 degrees C)
o All solutions at concentrations of 1 mol dm-3
Hess's law
Cycle to calculate enthalpies
Can also be shown by energy level diagrams
Standard enthalpies
Standard enthalpy of formation ^Hf enthalpy change when 1 mol of a substance is
formed from its elements in their standard states…read more

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