Physical chemistry Flashcards
Enthalpy
the thermal energy stored in a chemical system
law of conservation of energy
energy cannot be created or destroyed only moved from one place to another.
ΔH=
ΔHprod-ΔHreact
exothermic reaction
- enthalpy of product is smaller than reactants
- heat loss to the surroundings
- ΔH is negative
Endothermic reactions
- enthalpy of product is greater than reactants
- heat gain to system from the surroundings
- ΔH is positive
activation energy
the minimum energy required to start a reaction by breaking bonds in the reactants.
standard conditions
298K and 100kPa
enthalpy change of formation
the energy change that takes place when one mole of a compound is formed from its constituent elements
enthalpy change of combustion
energy change that takes place when one mole of a substance is completely combusted
enthalpy change of neutralsiation
the energy change where 1 mole of water is formed from a neutralisation reaction
q=
mcΔT
specific heat capacity
energy required to raise the temperature of a 1kg substance by 1k.
Average bond enthalpy
the average energy that is required for one mole of a gaseous bond to undergo homolytic fission
hess’s law
enthalpy change in a chemical reaction is independent to the route it takes
which way do arrows point in a Hess cycle when given combustion data?
Down
which way do arrows point in a Hess cycle when given formation data?
Up
effect of concentration on rate
increased concentration means more molecules in the same volume, meaning more frequent collisions, so rate increases
effect of pressure on rate
volume is reduced and molecules are brought closer together, so more frequent collisions so rate increases
what is a catalyst
a substance that increases the rate of a reaction without being used up in the process
