Energetics

Question 1

what is an exothermic reaction

Answer 1

Process of releasing heat energy for bond making is greater than absorbing heat energy for bond breaking

Question 2

what is an endothermic reaction

Answer 2

process of absorbing heat energy for bond breaking is greater than realising heat energy for bond making

Question 2

what does Mexo stand for

Answer 2

Making bonds
exothermic reaction

Question 2

what does Bendo stand for

Answer 2

breaking bonds
endothermic reaction

Question 2

breaking bonds diagram

Answer 2

the bonds absorb heat energy and then separate apart due to the energy

Breaking chemical bonds requires energy which is taken in from the surroundings in the form of heat

Question 2

forming bonds diagram

Answer 2

the molecules have to release heat energy to form bonds

Making new chemical bonds releases energy which radiates outwards from the reaction to the surroundings in the form of heat

Question 3

solid -> gas

Answer 3

sublimation
endothermic

Question 4

gas -> solid

Answer 4

deposition
exothermic

Question 5

solid -> liquid

Answer 5

melting
endothermic

Question 6

liquid -> solid

Answer 6

freezing
exothermic

Question 7

liquid -> gas

Answer 7

evaporation
endothermic

Question 8

gas -> liquid

Answer 8

condensation
exothermic

Question 9

whats a displacement reaction

Answer 9

more reactive element will displace the less reactive element in a compound

zinc + copper (ii) sulfate->zince sulfate +copper
zn(s) + CuSO₄ (aq) -> ZnSO₄ (aq) + Cu (s)
zinc-silver grey solid
copper sulphate- blue colour solution
zinc sulfate- colourless solution
copper- pinkish brown solid

Question 10

combustions , neutralisation and displacement

Answer 10

always exothermic

Question 11

Combustion reactions

Answer 11

Always exothermic
A substance reacts with oxygen
Energy (heat and often light) is released
Temperature of surroundings increases
Example:
Magnesium + oxygen → magnesium oxide + energy

Question 12

thermal decomposition and dissolving ammonium salt

Answer 12

endothermic reaction
(NH4​Cl)

Question 13

energy Level diagrams for exothermic reactions

Answer 13

Energy is released, so products have lower energy than reactants.
Y-axis: Energy
X-axis: Progress of reaction
Reactants: start higher
Products: finish lower
Activation energy (Eₐ): energy needed to start the reaction
ΔH: negative (arrow pointing down)
an exothermic reaction, the products have less energy than the reactants, so energy is released to the surroundings and the enthalpy change is negative.

Question 14

energy Level diagrams for endothermic reactions

Answer 14

Energy is absorbed, so products have higher energy than reactants.
What the diagram looks like (label this!)
Y-axis: Energy
X-axis: Progress of reaction
Reactants: start lower
Products: finish higher
Activation energy (Eₐ): energy needed to start the reaction
ΔH: positive (arrow pointing up)
How to describe it in words (exam-perfect ✨)
In an endothermic reaction, energy is taken in from the surroundings, so the products have more energy than the reactants and the enthalpy change is positive.

Question 15

what is a catalyst

Answer 15

A substance that speeds up a chemical reaction without being used up or chemically changed in the process.
Key points:
Lowers the activation energy (Eₐ) → reaction happens faster
Does not affect ΔH (the overall energy change of the reaction)
Can be reused many times