Enthalpy

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cody

Cards (16)

enthalpy is a measure of all heat energy in a chemical system
enthalpy change 
$\Delta H$ = H(products) - H(rectants)
exothermic change 
energy from system to surroundings
endothermic change 
energy from surroundings to system
exothermic - energy out of the system 
any energy loss from chemical system is balanced by same energy gain from the surroundings.
$\Delta$ H is negative
temperature of surroundings increases as they gain energy
endothermic - heat into the system 
chemical system that takes in heat energy from the surroundings
any energy gain is balanced by the same energy loss to the surroundings
∆H is positive
temperature of surroundings decrease as they lose energy
enthalpy change of formation 
enthalpy change that takes place when one mole of a compound is formed from its elements under standard conditions
standard enthalpy change of combustion 
enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions
when a substance reacts completely with oxygen the products are oxides of the elements in the substance
standard enthalpy change of neutralisation
energy change that accompanies the reaction of an acid by a base to form one mole of H2O under standard conditions
for enthalpy change of neutralisation the reaction involves H+ with OH- to form one mole of H2O
specific heat capacity  
energy required to raise the temperature of 1g of a substance by 1 K
average bond enthalpy 
energy required to break one mole of a specified type of bond in a gaseous molecule
bond enthalpies are always endothermic so always have a positive enthalpy value
bond breaking 
endothermic as energy is required
bond making 
exothermic because energy is released