Part I

Question 1

What are the standard conditions?

Answer 1

1. Temp: 25 degree
2. Pressure: 1 bar
3. Concentration: 1 mole dm3
4. Most stable physical forms

Question 2

Define standard enthalpy change of reaction

Answer 2

Change in enthalpy when molar quantities of reactants, as stated in stoichiometric equation, react together at 298K and 1bar

Question 3

Define standard enthalpy change of Formation

Answer 3

Change in enthalpy when one mole of a compound is formed from its constituent elements in their standard physical states at 298K and 1bar

Question 4

Define standard enthalpy change of Combustion

Answer 4

Heat evolved when one mole of a substance is completely burnt in excess oxygen at 298K and 1bar

Question 5

Define standard enthalpy change of neutralisation

Answer 5

Change in enthalpy when an acid reacts with a base to form one mole of water at 298K and 1bar

Question 6

Strong acid VS Weak acid

Answer 6

•Strong acid dissociate completely in water to give one mole of water

•Weak acid dissociate partially in water
=> energy is req’ed to complete the Parti all dissociation to give one mole of H+ so that one mole of water can be formed with one mole of OH-

Question 7

Define standard enthalpy change of Hydration

Answer 7

Heat evolved when one mole of the gaseous ions dissolved in water to form hydrated ions of infinite dilution at 298K and 1bar

Question 8

What are the 2 factors affecting hydration energy?

Answer 8

1. Charge: higher more heat

2. Size: smaller more heat

Question 9

Define standard enthalpy change of Solution

Answer 9

Change in enthalpy when one mole of a substance is dissolved in water to form a solution of infinite dilution at 298K and 1bar.

HCl(g)-> H+ + Cl-

• endo -> insoluble in water
• exdo -> soluble in water

Question 10

Define standard enthalpy change of Atomisation

Answer 10

Heat absorbed when one mole of gaseous atoms is formed from its element at 298K and 1bar

Na(a)-> Na(g)

Question 11

Define IE

Answer 11

Energy req’ed to remove one mole of the outermost electron from one mole of gaseous atoms of the element to form one mole of gaseous ions with a single positive charge

Question 12

Define EA

Answer 12

First: energy evolved when one mole of gaseous atoms accepts one mole of electrons to form one mole of gaseous singly charged negative ions

Cl(g)+ e- -> Cl- (g)

Question 13

Why is 1EA exo but 2EA endo?

Answer 13

1: attraction is formed between nucleus and the e- added
2: energy is req’ed to overcome the electrostatic repulsion of the incoming e- by the negative charge and anion

Question 14

Define LE

Answer 14

Heat evolved when one mole of the solid ionic compound is formed from its isolated gaseous ions at 298K and 1bar.

K+(aq) + Cl(aq)- -> KCl(s)

Question 15

Factors affecting LE?

Answer 15

1. Charge on ions
   - bigger=> more exo
2. Inter ionic distance
   - smaller ionic radius, shorter inter-ionic distance=> more exo

Question 16

Define Bond Energy

Answer 16

Energy required to break one mole of covalent bonds bt 2 atoms in a gaseous state

H-H (g) -> 2H(g)

**2X of atm

Question 17

Large and negative Δf suggests?

Answer 17

The cmpd is thermodynamically much more stable than its constituent elements