Enthalpy

Question 1

Can enthalpy be measure directly?

Answer 1

No

Question 2

Enthalpy change symbol

Answer 2

🔼H

Delta H

Question 3

Enthaply change definition

Answer 3

The enthalpy change of a reaction is the heat energy change with its surroundings at constant pressure.

Question 4

Enthalpy change units

Answer 4

kj mol^(-1)

Question 5

Delta meaning

Answer 5

Change

Question 6

Standard enthalpy changes are measured at…?

Answer 6

Standard pressure (100 kPa)
Standard temperature (298 K)

Symbol ΔHθ. But θ is superscript

Question 7

-ΔΗ is it exothermic or endothermic?

Answer 7

Exothermic

Question 8

+ΔΗ is it exothermic or endothermic?

Answer 8

Endothermic

Question 9

GRAPHS

Answer 9

SEE PAPER

Question 10

Standard enthalpy of reaction symbol

Answer 10

θ
ΔΗ
R

The r for reaction is replaced by a specific letter for particular standard enthalpies

Question 11

Standard enthalpy of Formation symbol

Answer 11

θ
ΔΗ
f

Question 12

Standard enthalpy of formation definition

Answer 12

This is the enthalpy change when 1 MOLE of a substance is FORMED from its ELEMENTS under standard conditions (100kPa and 298k) with all substances in their standard STATES (eg. Solid, liquid gas)

Question 13

Standard enthalpy of formation value of an element in its standard state

Answer 13

Must be 0

Question 14

Standard enthalpy of formation equation for H2O

Answer 14

H2 + 1/2 O2 ➡️ H2O

To form one mole of water

Question 15

Standard enthalpy of combustion symbol

Answer 15

θ
ΔΗ
c

Question 16

Standard enthalpy of combustion definition

Answer 16

This is the enthalpy change when 1 MOLE of a substance undergoes COMPLETE COMBUSTION under standard conditions (100kPa and 298K) with all substances being in their standard states

Question 17

What is meant by the term ‘standard states’ of a substance

Answer 17

Normal state at room temperature eg. Solid, liquid or gas

Question 18

What are standard conditions

Answer 18

100kPa (kilo pascals)

298K (kelvin)

Question 19

Standard enthalpy of combustion equation for CH4

Answer 19

CH4 + 2O2 ➡️ CO2 + 2H2O

Question 20

Standard enthalpy of atomization symbol

Answer 20

θ
ΔΗ
a

Question 21

Standard enthalpy of atomization definition

Answer 21

This is the enthaply change when 1 MOLE of GASEOUS ATOMS of a substance are FORMED from the substance in its standard state under standard conditions (100kPa and 298K)

Question 22

Standard enthalpy of atomization equation for chlorine

Answer 22

1/2 Cl2 (g) ➡️ Cl (g)

Cl2 is how is appears normally then Cl is the one mole that is formed

Question 23

Standard enthalpy of neutralization symbol

Answer 23

θ
ΔΗ
n

Question 24

Standard Enthalpy of neutralization definition

Answer 24

This is the Standard Enthalpy change when 1 MOLE of WATER is produced by the reaction of an ACID and a BASE under standard conditions (100kPa and 298K) with all substances being in their standard states

Question 25

Standard Enthalpy of neutralization equation for sulphuric acid and sodium hydroxide

Answer 25

BALANCED EQUATION. H2SO4 + 2NaOH ➡️ Na2SO4 + 2H2O
(Wrong as 2 moles of water)

Answer: 1/2 H2SO4 + NaOH ➡️ 1/2 Na2SO4 + H2O

Question 26

In an exotherimic reaction does it give out energy to its surroundings or take energy in? And does the temperature of the reaction decrease or increase?

Answer 26

Gives OUT energy to surroundings

Reaction temperature gies UP
so -ΔΗ as the products of the reaction end up with LESS energy than the reactants

Question 27

In an endothermic reaction does it give out energy to its surroundings or take energy in? And does the temperature of the reaction decrease or increase?

Answer 27

Takes IN energy from surroundings

Reaction temperature DEACREASES

Products have MORE energy than the reactants so ΔΗ is a positive value as

Question 28

Give the notation for an enthaply change under standard conditions at a temperature of 298K

Answer 28

θ
ΔΗ
298

Question 29

Describe the difference between endothermic and exothermic reactions

Answer 29

Exothermic gives OUT heat

Endothermic takes IN heat

Question 30

Enthalpy definition

Answer 30

The enthalphy of a system is a measure of the energy stored in (or heat content) of a system. Symbol H