DN 4). Enthalpy

Question 1

q=

Answer 1

mcΔT

Question 2

q means and units

Answer 2

enthalpy change in Joules

Question 3

m means and units

Answer 3

mass of substance in grams

Question 4

c means and units

Answer 4

specific heat capacity Jg^(-1)K^(-1)

Question 5

ΔT means and units

Answer 5

temperature change in ???? NOT SURE

Question 6

specific heat capacity

Answer 6

the amount of heat needed to raise the temperature of 1g of substance by 1K

Question 7

enthalpy change defintion

Answer 7

change in heat content at a constant pressure

Question 8

enthalpy definition

Answer 8

heat content of a substance

Question 9

Exothermic reaction

- A+B = C+D which has the greater enthalpy (A+B) or (C+D)

Answer 9

A+B

Question 10

Exothermic reaction

- the enthalpy change is…..

Answer 10

negative

Question 11

Exothermic reaction

- the temperature…..

Answer 11

increases

Question 12

Exothermic reaction

- what happens during the reaction

Answer 12

heat is lost to the surroundings

Question 13

Exothermic reaction

- what does the graph look like

Answer 13

reactants
                  |
                  |       ΔH = NEGATIVE
                  |
                  products

Question 14

Exothermic reaction

- two examples

Answer 14

oxidation of fuels

respiration

Question 15

Endothermic reaction

- A+B = C+D which has the greater enthalpy (A+B) or (C+D)

Answer 15

(C+D)

Question 16

Endothermic reaction

- the enthalpy change is…

Answer 16

positive

Question 17

Endothermic reaction

- the temperature….

Answer 17

decreases

Question 18

Endothermic reaction

- what happens during the reaction

Answer 18

heat is gained from the surroundings

Question 19

Endothermic reaction

- what does the graph look like

Answer 19

products      
                                |
                                |    ΔH = POSITIVE
                                |  
        reactants

Question 20

Endothermic reaction

- two examples

Answer 20

photosynthesis

thermal decomposition

Question 21

what does Ø mean (line through should be horizontal

Answer 21

standard conditions

Question 22

what are Ø (the standard conditions)

Answer 22

100KPa

298K or 25degrees c

Question 23

what does ΔHf^Ø mean

Answer 23

standard enthalpy of formation

Question 24

standard enthalpy of formation defintion

Answer 24

enthalpy change when 1 mole of substance is formed from it’s constituent elements under standard conditions and in their standard states

Question 25

write ΔHf^Ø(H2O)

Answer 25

H2(g) + 1/2O2(g) –> H2O(l)

Question 26

what does ΔHc^Ø mean

Answer 26

the standard enthalpy of combustion

Question 27

standard enthalpy of combustion defintion

Answer 27

enthalpy change when 1 mole of substance is completely burned in oygen under standard conditions with all substances in standard state

Question 28

write ΔHc^Ø(CH4)

Answer 28

CH4(g) + 2O2(g) –> CO2(g) + 2H2O(l)

Question 29

enthalpy change (per mole) calculation

Answer 29

q / number of moles reacting

Question 30

with extrapolating graphs, how to find ΔT

Answer 30

extrapolate top and bottom lines
at the point where there is no measurement (cause this is where the reactants were added) find the vertical difference between the two lines

Question 31

what does hess’ law state

Answer 31

the enthalpy change for a reaction is dependent only on enthalpy of the reactants and prodicts and not the root taken

Question 32

to use ΔHf^Ø values arrows go…

Answer 32

outwards

Question 33

CRP (crap)

Answer 33

when using combustion values ΔH = sum of reactants - sum of products
opposite = FPR

Question 34

to use ΔHc^Ø values arrows go…

Answer 34

down / inwards