3.2

Question 1

Enthalpy = ?

Answer 1

Measure of heat energy in a chemical system

🔼H = H(products) - H(reactants)

Energy is conserved

Question 2

Exothermic

Answer 2

🔼H = NEGATIVE (exo)

Heat to surroundings
Temp of surroundings increases

Question 3

Endothermic

Answer 3

🔼H = POSITIVE (endo)

Heat from surroundings
Temp of surroundings decreases

Question 4

0 degrees = how many K?

Answer 4

0 degrees = 273 K

Question 5

Ideal gas equation

Answer 5

q=mc🔼T

could be inaccurate due to heat loss to surroundings, incomplete reaction/combustion, or not standard conditions

Question 6

Activation energy = ?

Answer 6

The minimum energy required for a reaction to take place

Ea

Question 7

Standard conditions = ?

Answer 7

25 degrees C

100kPa (1atmosphere)

1moldm-3

Question 8

Average bond enthalpy = ?

Answer 8

The energy required to break 1 mole of bonds in a gaseous molecule

• energy required to break bonds
• bond enthalpies always ENDOTHERMIC = 🔼H+ve

Question 9

Bond breaking

Answer 9

Endothermic

🔼H+ve

Energy required to break bonds is greater that the energy released making them

Question 10

Bond forming

Answer 10

Exothermic

🔼H-ve

Energy released making bonds is greater than energy required breaking them

Question 11

Hess’ law = ?

Answer 11

States that enthalpy changes and be determined indirectly

Route1=Route2
A+B=C

Question 12

Rate of reaction = ?

Answer 12

Rate = change in concentration ➗ time

Affected by:
• concentration/pressure
• temperature 
• SA of solid reactants 
• presence of a catalyst

Question 13

Ineffective / effective collisions

Answer 13

Ineffective:
No reactions (right particles didn’t collide)

Effective:
Reaction (right particles collide)

Question 14

How to follow the progress of a reaction

Answer 14

Monitor removal of reactant
Follow formation of the product
Gas: volume produces, or loss of mass of reactants

Question 15

definition of a CATALYST

Answer 15

A substance that changed the rate of a chemical reaction without undergoing any permanent change itself

• not used up
• provides surface for reaction
• regenerated at the end

Provides an alternative route for a reaction with a LOWER ACTIVATION ENERGY

Question 16

Homogenous catalyst = ?

Answer 16

SAME physical state as reactants

Question 17

Heterogenous catalyst = ?

Answer 17

DIFF physical state from the reactants (absorption and desorption)

Question 18

The Boltzmann distribution

Answer 18

After Ea = small proportion of molecules have more than the Ea which is enough energy to react

• no molecules have 0 energy
• area under curve = total no. molecules
• no maximum energy of a molecule

Question 19

Boltzmann distribution; increasing temperature

Answer 19

• lower peak

* more molecules have the Ea (higher rate of reaction)

Question 20

Boltzmann distribution; addition of a catalyst

Answer 20

• same curve as normal
• lower Ea
• more molecules have a new lower Ea

Question 21

Dynamic equilibrium

Answer 21

Rate of forward = rate of backward
Dynamic = both taking place
Closed system = isolated from surroundings

Question 22

Le Chatelier’s principal

Answer 22

States that if a equilibrium system is subjected to external change, the system readjusts itself to minimise the effect of said change

Question 23

Equilibrium; changing the temp

Answer 23

Increasing temp:
Will change to favour the ENDO reaction (🔼H+ve)

Decreasing temp:
Will change to favour EXO reaction (🔼H-ve)

Question 24

Equilibrium constant Kc = ?

Answer 24

Kc =

[C]c [D]d (products)
➗
[A]a [B]b (reactants)

When
aA + bB <> cC + dD

Question 25

Kc values

Answer 25

Greater than 1 = positioned towards the products

Less than 1 = positioned towards the reactants