DN 4). Enthalpy Flashcards Preview

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Flashcards in DN 4). Enthalpy Deck (34):
1

q=

mcΔT

2

q means and units

enthalpy change in Joules

3

m means and units

mass of substance in grams

4

c means and units

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

5

ΔT means and units

temperature change in ???? NOT SURE

6

specific heat capacity

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

7

enthalpy change defintion

change in heat content at a constant pressure

8

enthalpy definition

heat content of a substance

9

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

A+B

10

Exothermic reaction
- the enthalpy change is.....

negative

11

Exothermic reaction
- the temperature.....

increases

12

Exothermic reaction
- what happens during the reaction

heat is lost to the surroundings

13

Exothermic reaction
- what does the graph look like

reactants
|
| ΔH = NEGATIVE
|
products

14

Exothermic reaction
- two examples

oxidation of fuels
respiration

15

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

(C+D)

16

Endothermic reaction
- the enthalpy change is...

positive

17

Endothermic reaction
- the temperature....

decreases

18

Endothermic reaction
- what happens during the reaction

heat is gained from the surroundings

19

Endothermic reaction
- what does the graph look like

products
|
| ΔH = POSITIVE
|
reactants

20

Endothermic reaction
- two examples

photosynthesis
thermal decomposition

21

what does Ø mean (line through should be horizontal

standard conditions

22

what are Ø (the standard conditions)

100KPa
298K or 25degrees c

23

what does ΔHf^Ø mean

standard enthalpy of formation

24

standard enthalpy of formation defintion

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

25

write ΔHf^Ø(H2O)

H2(g) + 1/2O2(g) --> H2O(l)

26

what does ΔHc^Ø mean

the standard enthalpy of combustion

27

standard enthalpy of combustion defintion

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

28

write ΔHc^Ø(CH4)

CH4(g) + 2O2(g) --> CO2(g) + 2H2O(l)

29

enthalpy change (per mole) calculation

q / number of moles reacting

30

with extrapolating graphs, how to find ΔT

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

31

what does hess' law state

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

32

to use ΔHf^Ø values arrows go...

outwards

33

CRP (crap)

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

34

to use ΔHc^Ø values arrows go...

down / inwards