Energy

Question 1

What are the sequences of processes that occur in any reaction?

Answer 1

1. Add reactants together.
2. Reactants take in required energy from surroundings to break their bonds (activation energy, endothermic part).
3. Free electrons collide together to form new bonds, releasing energy (exothermic part).
4. Enthalpy change (ΔH) = Energy of reactants – Energy of products.

Question 2

What is activation energy in a reaction?

Answer 2

Activation energy is the energy required to break the bonds in the reactants. It is the endothermic part of the reaction.

Question 3

What is enthalpy change in a reaction?

Answer 3

Enthalpy change = Energy of reactants – Energy of products.

• A negative value indicates an exothermic reaction.
• A positive value indicates an endothermic reaction.

Question 4

Define exothermic and endothermic reactions.

Answer 4

• Exothermic: A reaction that releases energy to its surroundings.
• Endothermic: A reaction that absorbs energy from its surroundings.

Question 5

How do you explain whether a reaction is exothermic or endothermic in terms of bonds?

Answer 5

• Exothermic: Energy released during bond making is greater than energy absorbed during bond breaking.
• Endothermic: Energy released during bond making is less than energy absorbed during bond breaking.

Question 6

What are some reasons why experimental data might differ from theoretical values?
Back:

Answer 6

1. Heat is lost to surroundings.
2. Impure substances are used.
3. Incomplete combustion.

Question 7

How do you draw an exothermic or endothermic reaction diagram?

Answer 7

1. Identify if the reaction is exothermic or endothermic.
2. Label reactants and products.
   * For exothermic: Products have lower energy than reactants.
   * For endothermic: Products have higher energy than reactants.

Question 8

How do you calculate the total energy produced in a reaction?

Answer 8

Use the equation:
Q = mcΔT

• m: Mass or volume of water or solutions used in the experiment.
• c: Specific heat capacity (4.2 J/g°C for water).
• ΔT: Rise in temperature.

This gives energy in joules (J).

Question 9

How do you calculate enthalpy change (ΔH)?

Answer 9

Method 1: ΔH = Energy of reactants – Energy of products.
* If ΔH is negative, the reaction is exothermic.

Method 2: Molar enthalpy change = Energy in kJ / Number of moles.
* ΔH = Q (kJ) / Moles.