Unit 3 - Equilibria & Chemical Energy

Question 1

What does adding a reactant/ removing a product do to effect the equilibrium

Answer 1

• Equilibrium will shift right
• Increased concentration of products
• Favours forward reaction

Question 2

What does adding a product/ removing a reactant do to effect the equilibrium

Answer 2

• Equilibrium shifts left
• Increases concentration of reactants
• Favours backwards reaction

Question 3

How does increasing temperature affect the equilibrium

Answer 3

• Increasing temperature favours endothermic reaction
• Equilibrium favours direction of endothermic reaction

Question 4

How does decreasing temperature effect equilibrium

Answer 4

• Decreasing temperature favours exothermic reaction
• Equilibrium moves in direction of exothermic reaction

Question 5

Is enthalpy change positive or negative for an endothermic reaction?

Answer 5

Positive

Question 6

Is enthalpy change positive or negative for an exothermic reaction?

Answer 6

Negative

Question 7

What are the bewares for equilibrium concentration?

Answer 7

• Adding an H ion where OH is involved in reaction causes neutralisation reaction
• Adding H ion when H is involved increases concentration of opposite reaction
• Adding AgNO₃ forms precipitate reactions

Question 8

How does decreasing pressure effect equilibrium

Answer 8

• More volume
• Favours reaction which produces more gas volumes

Question 9

How does increasing pressure effect equilibrium

Answer 9

• Less volume
• Favours reaction which produces smaller gas volumes

Question 10

How does adding a catalyst effect equilibrium

Answer 10

Only increases the rate equilibrium is achieved

Question 11

For enthalpy of combustion questions, are answers positive or negative

Answer 11

Negative

Question 12

State Hess’s law

Answer 12

The enthalpy change of a chemical reaction is independent of the route taken

Question 13

Are breaking bonds endothermic or exothermic

Answer 13

Endothermic (+ve)

Question 14

Are making bonds endothermic or exothermic

Answer 14

Exothermic (-ve)

Question 15

What’s the formula for enthalpy change for bond enthalpy questions

Answer 15

🔺H = Bonds Broken(+ve) + Bonds made (-ve)

Question 16

What is the difference between bond enthalpy and mean bond enthalpy

Answer 16

• Molar bond enthalpy is the energy required to break one mole of bonds in a diatomic molecule.
• Mean molar bond enthalpy is the energy required to break one mole of bonds that occur in compounds

Question 17

What happens if you add lime water to an equation featuring CO2 as a reactant?

Eg. Adding lime water to this equation: CO2 + O2 ↔️ H2O

Answer 17

Lime water removes CO2. Equilibrium shifts left to create more CO2.

Question 18

What happens if you add an ion to a chemical reaction featuring a metal ion?

Answer 18

If you add an ion that will form a precipitate with the metal ion, (check solubility table) it will remove it from the system.

Question 19

What happens if you add a silver ion to a halide ion (eg. Cl-) ?

Answer 19

It will form a precipitate and remove the halide ion from the system.