3.2.1 enthalpy changes

Question 1

what is enthalpy change of combustion

Answer 1

enthalpy change when one mole of a substance burns completely in excess oxygen under standard conditions

Question 2

what are standard conditions

Answer 2

298K
101Kpa

Question 3

what is carbon in its standard state

Answer 3

solid

Question 4

what is iodine at room temperature and pressure

Answer 4

solid

Question 5

how do you calculate energy released

Answer 5

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

Question 6

why is the experimental value less than the published value in combustion

Answer 6

-energy is lost to the surroundings
-non standard conditions
-incomplete combustion of fuel

Question 7

what is enthalpy change of formation

Answer 7

enthalpy change when one mole of a compound is formed from its elements in their standard states under standard conditions

Question 8

what is enthalpy change of neutralisation

Answer 8

enthalpy change when one mole of water is formed in a neutralisation reaction

Question 9

how do you calculate enthalpy change of neutralisation

Answer 9

LOOK IN BOOKLET

Question 10

what is the energy required to break bonds in an exothermic reaction

Answer 10

the energy required to break bonds is less than the energy given out when new bonds form

Question 11

what is the energy required to break bonds in an endothermic reaction

Answer 11

the energy required to break bonds is more than the energy given out when new bonds form

Question 12

is bond making endo or exothermic

Answer 12

exothermic

Question 13

is bond breaking endo or exothermic

Answer 13

endothermic

Question 14

draw an enthalpy profile for an exothermic reaction

Answer 14

in booklet

Question 15

draw an enthalpy profile for an endothermic reaction

Answer 15

in booklet

Question 16

describe the experiment to determine enthalpy change of combustion of a fuel

Answer 16

1. 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
2. mass of water in the can
3. start and final temperature of water which allows temperature change to be calculated

Question 17

where do formation arrows point

Answer 17

arrows point up

Question 18

where do combustion arrows point

Answer 18

arrows point down

Question 19

how to calculate bond enthalpies

Answer 19

products-reactants=enthalpy change of formation

Question 20

what does the term average bond enthalpies mean

Answer 20

in ms

Question 21

which moles do you use when you have the enthalpy of neutralisation

Answer 21

if its a 1:1 ratio- use the smallest number of moles
if its a 1:2 ratio use the limiting factor