3.2.1 enthalpy changes Flashcards
what is enthalpy change of combustion
enthalpy change when one mole of a substance burns completely in excess oxygen under standard conditions
what are standard conditions
298K
101Kpa
what is carbon in its standard state
solid
what is iodine at room temperature and pressure
solid
how do you calculate energy released
E=mCat
m=mass of water
gives answer in J you need to convert to KJ
calculate moles of fuel burnt
n=m/mr
divide top answer by bottom
DONT FORGET SIGN
why is the experimental value less than the published value in combustion
-energy is lost to the surroundings
-non standard conditions
-incomplete combustion of fuel
what is enthalpy change of formation
enthalpy change when one mole of a compound is formed from its elements in their standard states under standard conditions
what is enthalpy change of neutralisation
enthalpy change when one mole of water is formed in a neutralisation reaction
how do you calculate enthalpy change of neutralisation
LOOK IN BOOKLET
what is the energy required to break bonds in an exothermic reaction
the energy required to break bonds is less than the energy given out when new bonds form
what is the energy required to break bonds in an endothermic reaction
the energy required to break bonds is more than the energy given out when new bonds form
is bond making endo or exothermic
exothermic
is bond breaking endo or exothermic
endothermic
draw an enthalpy profile for an exothermic reaction
in booklet
draw an enthalpy profile for an endothermic reaction
in booklet
describe the experiment to determine enthalpy change of combustion of a fuel
- mass of fuel and burner are measured at the start and end of the experiment. This allow the mass of fuel to be calculated and the moles of fuel burnt to be calculated
- mass of water in the can
- start and final temperature of water which allows temperature change to be calculated
where do formation arrows point
arrows point up
where do combustion arrows point
arrows point down
how to calculate bond enthalpies
products-reactants=enthalpy change of formation
what does the term average bond enthalpies mean
in ms
which moles do you use when you have the enthalpy of neutralisation
if its a 1:1 ratio- use the smallest number of moles
if its a 1:2 ratio use the limiting factor