Energetics

Question 1

Exothermic Reactions

Answer 1

Definition: A reaction that gives out heat to the surroundings is said to be exothermic.

So, as the reactants are converted to products, they lose energy as heat, which is transferred to the surroundings, which increases the temperature.

Question 2

Enthalpy Change

Answer 2

The amount of heat energy taken in or given out in a chemical reaction.

Symbol: ΔH

The difference in energy between the reactants and the products.

Measured in reference to reaction, not surroundings. So… value of enthalpy change always negative.

Question 3

Examples of Exothermic Reactions

Answer 3

Any combustion reactions
Any metals + acids
Any neutralisation reactions

Question 4

Conservation of Energy

Answer 4

Energy cannot be created or destroyed, but it can be transferred and stored. See closed and open systems.

Question 5

Closed and Open Systems

Answer 5

In a closed system, energy is conserved. In an open system, energy can be lost or gained from the surroundings.

Question 6

Endothermic Reactions

Answer 6

Definition: A reaction that takes in heat from the surroundings is said to be endothermic.

So, as the reactants are converted to products, they gain energy as heat, which is transferred from the surroundings, which increases the temperature of the products.

Question 7

Examples of Endothermic Reactions

Answer 7

Photosynthese
Melting and Evaporating
Boiling an egg

Question 8

Bond Energies

Answer 8

The aount of energy required to break a bond is eqaul to the energy released when the SAME bond is created.

Bond energy values are given in kJ/mol
Kilojoules per mole

Question 9

Heat energy

Answer 9

heat energy = mass x specific heat capacity x change in temperature

Question 10

Energy Level Diagrams

Answer 10

https://online-learning-college.com/wp-content/uploads/2022/06/Energy-level-diagrams-.jpg
activation energy - the minimum amount of energy required to start a reaction.
It is needed to break the bonds of the reactants.