enthaply changes Flashcards
(18 cards)
what is enthalpy changes
the enthalpy change of a reaction is the heat change in the reaction at constant pressure
standard conditions for enthalpy
100 kpa
298 ( 25degree )
endothermic
reactions that absorb energy from the surroundings
enthaply changes is positive
exothermic
reactions that release energy to the surroundings
ethaply changes is negative
standard enthaply change of reaction
the enthaply change of a reaction is the enthaply change when the number of moles of reactants as specified in the balanced equation react together
standard enthaply of neutralisation
the enthalpy change when an acid and alkali react to form 1 mole of water under standard conditions
standard enthaply change of formation
the enthalpy change when one mole of a compound is formed from its elements in their standard states under standard conditions
standard enthalpy of combustion
enthaply change when 1 mole of a substance is completely burned in oxygen to make CO2 and H2O under standard conditions
bonds broken
to break a bond energy needs to be absorbed
bonds are broken in the reactants and this is a endothermic process
bonds made
when bonds are formed energy is released
bonds are made when products are produced and this is exothermic
equation for enthaply changes
enthaply change = total energy to break bonds - total energy to be released
calorimetry definition
is used to work out the enthaply change of combustion
energy changes equation
q = m x c x temp change
mean bond enthaply
the mean bond enthaply is the enthaply change when one mole of bonds ( gaseous compounds) bonds is broken
bond energy equation
bond energy = bond energy broken - bond energy made
define hess’s law
the total enthaply change for a reaction is independent of the route by which the chemical change takes place
what is hess’s law used for
its used to work out the enthaply change to form a hydrated salt from an anhydrous salt
enthaply equation
Enthaply = Q / no of moles
