Enthalpy changes Flashcards
what is the enthalpy charge of a reaction
the heat change in a reaction at constant pressure
what is the symbol for enthalpy change and the units
(draw) kJmol-1
what are endothermic reactions and what will there value always be give an example
reactions that take in energy from surroundings, always positive, decomposition of calcium carbonate
what are exothermic reactions, what will their value always be and give an example
reactions that release energy, value is negative, combustion of ethane
what is the standard enthalpy change of neutralisation
the enthalpy change when an acid and alkali react to form 1 mole of water under standard conditions
what is the standard enthalpy change of combustion
the enthalpy change when 1 mole of a substance is completely burned in oxygen ti make CO2 and H2O under standard conditions
what is the standard enthalpy change of formation
the enthalpy change when 1 mole of a compound is formed from its elements in their standard states under standard conditions
if more energy is required to break bonds than energy given out when bonds are formed the reaction is
endothermic
if more energy is released when making bonds than needed to break bonds the reaction will be
exothermic
how do you calculate enthalpy change
(total energy to break bonds)- (total energy released arming bonds)
how do you calculate energy from a calorimetry experiment
q=mc^t
q= energy lost or gained (J)
m= mass o water or solution (g)
c=specific heat capacity= 4.18
T= temperature change (K)
enthalpy= q/moles
what is Hess’s law
the total enthalpy change of a reaction is independent of the route taken
what is a formation cycle
reactions—– products
elements
In their standards states
arrows go upwards
what is a combustion cycle
reaction——–products
combustion products
always co2 and h2o
arrows face downwards
