Energetics Flashcards
what is enthalpy change?
the heat transferred in a reaction at constant pressure
what are standard conditions?
100kpa
298k
what is an exothermic reaction?
energy is given out to the surroundings so the temperature goes up,and products have less energy than reactants
what is an endothermic reaction?
takes in energy from the surroundings ,temp falls, the products have more energy than reactants.
what is the standard enthalpy of combustion?
the enthalpy change when 1 mole of substance is completely burned in oxygen under standard conditions with all reactants and products in their standards states
what is the standard enthalpy of formation?
the enthalpy change when 1 mole of compound is formed from its constituent elements in their standard states under standard conditions.
what is mean bond enthalpy?
the average enthalpy need to break different types of molecules
how do you calculate the enthalpy change of a reaction?
bonds broken-bonds formed
why do mean bond enthalpy calculations differ from hess law?
(MBE) only uses averages which is less accurate
what charge is an exothermic reaction
-
what charge is an endothermic reaction
+
why is the standard formation of barium and aluminum 0
they are elements
what are problems with the calorimetry
- heat is absorbed by container
- heat is lost to surroundings
what are problems with the flame calorimeter
- combustion may be incomplete
- some flammable liquid may escape by evapouration
what is the difference between heat and temperature
heat is a measure of total energy while temp is the average Ke
state hess’ law
the total enthalpy change for a reaction is independent of the route taken
how do you calculate enthalpy change of formation with hess law
-write under the reation list of all the elemts involved
-label the arrows pointing up
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-use formula AH^1=AH^2+AH^3
how do you workout the enthalpy change of combustion with hess law
arrows point towards combustion products
-
what does q=mcAT mean
q=heat loss/gained
m=mass(g)
c=specific heat capacity
AT=change in temperature(k)
what is the units for hess’ law
kjmol-1
how do u calculate the standard enthalp of combustion using the actual heat change in reaction
q/no. of moles
what is a flame calorimeter used for
measure the heat energy produced in a combustion reaction
