Chemistry Paper 1 #2

Question 1

What is the formula for calculating the energy change in a reaction using bond energies?

Answer 1

Energy change = Sum of bond energies of bonds broken - Sum of bond energies of bonds made.

Question 2

How do you determine if a reaction is exothermic or endothermic from bond energy calculations?

Answer 2

If the energy change is negative, the reaction is exothermic. If positive, the reaction is endothermic.

Question 3

Write the half-equation for the reaction at the cathode during the electrolysis of aqueous copper(II) sulfate.

Answer 3

Cu²⁺ + 2e⁻ → Cu

Question 4

Write the half-equation for the reaction at the anode during the electrolysis of aqueous copper(II) sulfate.

Answer 4

4OH⁻ → O₂ + 2H₂O + 4e⁻

Question 5

Balance the equation for the reaction between sodium and water: Na + H₂O → NaOH + H₂

Answer 5

2Na + 2H₂O → 2NaOH + H₂

Question 6

Write the ionic equation for the reaction between magnesium and hydrochloric acid.

Answer 6

Mg + 2H⁺ → Mg²⁺ + H₂

Question 7

Write the balanced equation for the reaction between sulfuric acid and sodium hydroxide.

Answer 7

H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O

Question 8

What is the result of mixing hydrochloric acid with potassium hydroxide?

Answer 8

They react to form potassium chloride and water (KCl + H₂O).

Question 9

Why is carbon used in the extraction of metals like iron?

Answer 9

Carbon is used to reduce iron oxide to iron, as it is more reactive than iron but cheaper than electrolysis.

Question 10

Explain why gold does not corrode or react easily.

Answer 10

Gold is a very unreactive metal, so it does not react with water or oxygen, making it resistant to corrosion.

Question 11

What is a half-equation for the anode reaction in a hydrogen fuel cell?

Answer 11

2H₂ → 4H⁺ + 4e⁻

Question 12

What are two environmental advantages of using hydrogen fuel cells?

Answer 12

They produce only water as a by-product and have higher energy efficiency than traditional combustion engines.

Question 13

Differentiate between a concentrated and a dilute solution.

Answer 13

A concentrated solution has a high amount of solute per volume of solvent, while a dilute solution has a low amount of solute.

Question 14

What is meant by homolytic fission in bond enthalpy?

Answer 14

Homolytic fission is the process of breaking a bond evenly so that each atom takes one electron, forming radicals.

Question 15

Explain the purpose of an energy level diagram in reactions.

Answer 15

An energy level diagram shows the energy absorbed or released during a reaction, indicating whether it is exothermic or endothermic.

Question 16

How does an electrolyte function in an electrochemical cell?

Answer 16

An electrolyte conducts electricity by allowing ions to move, facilitating redox reactions at the electrodes.

Question 17

What is activation energy, and why is it important?

Answer 17

Activation energy is the minimum energy required to start a reaction by breaking initial bonds; it determines the reaction’s rate.

Question 18

Define oxidation in terms of electron transfer.

Answer 18

Oxidation is the loss of electrons from a substance during a chemical reaction.

Question 19

Define reduction in terms of electron transfer.

Answer 19

Reduction is the gain of electrons by a substance during a chemical reaction.

Question 20

Explain why copper can be found naturally as an uncombined element.

Answer 20

Copper is relatively unreactive and doesn’t readily form compounds, allowing it to be found in its elemental form in nature.

Question 21

What is meant by ‘standard electrode potential’?

Answer 21

Standard electrode potential is the voltage measured under standard conditions when a half-cell is connected to a standard hydrogen electrode.