3) Energy changes in industry

Question 1

How to calculate kelvin (K)?

Answer 1

⁰C to K = +273

Question 2

What is the symbol for standard conditions?

Answer 2

⦵

Question 3

What are the standard conditions?

Answer 3

Pressure-kPa
Temp- 293K (25C)
Concentration- 1 moldm-3

All reactants and products are in their standard states.

Question 4

What is an exothermic reaction?

Answer 4

Exothermic reactions give out heat energy to the surroundings

Question 5

What is an endothermic reaction?

Answer 5

Endothermic reactions take in energy from the surroundings

Question 6

Why do exothermic reactions give out heat to their surroundings?

Answer 6

This is because the enthalpy of the products being made is smaller than the enthalpy of the reactants being used so the excess heat is released.

Question 7

Why do endothermic reactions take in heat from their surroundings?

Answer 7

This is because the enthalpy of the products being made is bigger than the enthalpy of the reactants being used so additional heat is required from the surrounding area.

Question 8

Are endothermic/exothermic have a positive/negative enthalpy change?

Answer 8

Exothermic- Negative Enthalpy change
Endothermic- Positive enthalpy change

Question 9

What is enthalpy?

Answer 9

Heat content of reactions.

Question 10

Why do exothermic reactions have a negative ΔH?

Answer 10

Because heat energy has been lost from the chemical system and released into the surroundings

Question 11

Why do endothermic reactions have a positive ΔH?

Answer 11

Because heat energy has been gained by the chemical system from the surroundings

Question 12

What activation energy?

Answer 12

The energy required for the reaction to take place (shown as Ea)

Question 13

How do catalysts affect rate of reaction?

Answer 13

Catalysts increase the rate of chemical reactions by providing an alternative reaction route with a lower activation energy

Question 14

What are the advantages of catalysts?

Answer 14

Don’t get used up
Can be reused

Question 15

What are the two stages to dissolving an ionic solid?

Answer 15

Step 1: Breaking down the ionic lattice
Step 2: Hydration of the ions by water molecules

Question 16

How is breaking down the ionic lattice endothermic?

Answer 16

Breaking down an ionic lattice requires a large input in energy in order to break the strong electrostatic forces of attraction between the oppositely charged ions. This process is therefore endothermic

Question 17

What occurs during hydration?

Answer 17

The positive ions will be attracted to the δ- oxygen atom in the water molecules

The negative ions will be attracted to the δ+ hydrogen atoms in the water molecules

The water molecules will completely surround the ions

Question 18

Why is hydration of the ions by water molecules exothermic?

Answer 18

This process involves the formation of new bonds therefore energy is released and therefore hydration of ions is always exothermic

Question 19

What 2 things is the magnitude of the enthalpy change of hydration dependent on?

Answer 19

1)The size of the ions
2) The charge of the ions

Question 20

How does the size of the ion affect the magnitude of the enthalpy change of hydration?

Answer 20

The smaller the ion the more exothermic the enthalpy change of hydration. This is because smaller ions have a higher charge density and can get closer to the water molecules. Therefore there is a stronger attraction between the ions and the water molecules

Question 21

How does the charge of the ion affect the magnitude of the enthalpy change of hydration?

Answer 21

The higher the charge of the ion the more exothermic the enthalpy change of hydration. This is because ions with higher charges have a higher charge density and can get closer to the water molecules and are able to attract them more strongly