Exo and Endothermic Reactions

• Chemistry
• Secondary Education
• Age 12,13

Exothermic and Endothermic Reactions

Topic 6. Chemical Energetics 

06 March 2024

• construct a poster to describe an exothermic or endothermic reaction
• write chemical equations to show an exothermic or endothermic reaction

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Product/Output - Kahoot results.

Standards - Correct responses.

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Exothermic and Endothermic Reactions

Topic 6. Chemical Energetics 

06 March 2024

Exothermic and Endothermic Reactions

Topic 6. Chemical Energetics 

06 March 2024

What's the difference?

physical process

chemical reaction

physical process

chemical reaction

Exo Physical process - dissolving MgCl2 in water

Exo Chemical reaction - adding zinc to copper (II) sulfate

Exo Process - releases heat or thermal energy TO the surroundings

Endo Process - takes in heat energy FROM the surroundings

Exothermic and Endothermic Reactions

Topic 6. Chemical Energetics 

06 March 2024

reactants

product

reactants

product

carbon + 2 oxygen

carbon dioxide

C(s) + O2 (g)

CO2 (g)

Types of Chemical Reactions

Exothermic and Endothermic Reactions

Topic 6. Chemical Energetics 

06 March 2024

reactants

product

carbon + 2 oxygen

carbon dioxide

C(s) + O2 (g)

CO2 (g)

The thermal energy (heat) content of a system

Enthalpy, H

The transfer of thermal energy during a reaction

Enthalpy change, Δ H

Delta = change in

Delta = change in

ΔH = (bond-breaking energy) - (bond-making energy)

How do we calculate the 

enthalpy change of the reaction?

Bond energy = the energy needed to break a particular type of covalent bond

Delta = change in

reactants

product

carbon + 2 oxygen

carbon dioxide

C(s) + O2 (g)

CO2 (g)

ΔH = (bond-breaking energy) - (bond-making energy) kJ/mol

ΔH = (0 + 498) - (2x 803)

ΔH = (498) - (1606)

ΔH = -1108 kJ/mol = exothermic

C(s) + O2 (g)

CO2 (g)   ; ΔH = -1108 kJ/mol 

Exothermic and Endothermic Reactions

Topic 6. Chemical Energetics 

06 March 2024

Reaction Pathway Diagrams (Reaction Profiles)

• Used to represent the energy changes involved in a chemical reaction

Step 1 :    Draw and label the x and y axes.

Step 2 :    Write the chemical equation.

Step 3 :    Identify whether it is an exothermic or endothermic reaction.

Step 4 :    Draw the line for the reactant. Write the reactant symbols.

Step 5 :    Draw the line for the product. Write the product(s) symbols.

Step 6 :    Draw the arrow for the energy released or absorbed.

reactants

product

carbon + 2 oxygen

carbon dioxide

C(s) + O2 (g)

CO2 (g)

ΔH = (total energy needed) - (total energy given out) kJ/mol

ΔH = (0 + 498) - (2x 803)

ΔH = (498) - (1606)

ΔH = -1108 kJ/mol = exothermic

C(s) + O2 (g)

CO2 (g)   ; ΔH = -1108 kJ/mol 

(kJ/mol)

(kJ/mol)

(kJ/mol)

C(s) + O2 (g)

(kJ/mol)

C(s) + O2 (g)

CO2 (g)

(kJ/mol)

the minimum energy required to start a chemical reaction - for a reaction to take place the colliding particles must have at least this amount of energy

Activation energy, Ea

Exothermic and Endothermic Reactions

Topic 6. Chemical Energetics 

06 March 2024

reactants

product

water

hydrogen + oxygen

2H2O(l)

2H2(g) + O2 (g)

ΔH = (total energy needed) - (total energy given out) kJ/mol

ΔH = [4x 464)] - [(2x 436) + 498]

ΔH = (1856) - (1370)

ΔH = +486 kJ/mol = endothermic

Example 2: Hydrolysis of water molecule into hydrogen gas and oxygen gas

2H2O(l)

2H2(g) + O2 (g)  ; ΔH = +486 kJ/mol 

(kJ/mol)

Exothermic and Endothermic Reactions

Topic 6. Chemical Energetics 

06 March 2024

• Goal and Expected Output: Given your chosen chemical reactions, you must make an info poster containing the following important details:
• - Reactants
• - Products
• - Word equation
• - Symbol equation
• - Enthalpy change of the reaction (calculated using bond energies) 
• - Endothermic or exothermic?
• - Making bonds or Breaking bonds?
• - Reaction Pathway diagrams with activation energy
• Standards : Interpretation of Reaction Pathway Diagrams, Explanation of Enthalpy Change, Understanding of Activation Energy, Creation of Reaction Pathway Diagrams

Collaborative Activity

• Share your outputs.
• What similarities and differences have you noticed?

Wrap-up

Exothermic and Endothermic Reactions

Topic 6. Chemical Energetics 

06 March 2024

• Share the results of your experiment.
• What similarities and differences have you noticed?

Wrap-up

Example 1:

STEPS:

Step 1 : Draw and label the x and y axes.<div>Step 2 : Write the chemical equation.</div><div>Step 3 : Identify whether it is an exothermic or endothermic reaction.</div><div>Step 4 : Draw the line for the reactant.</div><div>Step 5 : Draw the line for the product.</div><div>Step 6 : Draw the arrow for the energy released or absorbed.</div>

CH₄ (g) + O₂ (g) → CO₂ (g) + 2H₂O (l)          △H = - 891 kJ/mol

Prac 2.4 - Types of chemical reactions

Topic 6. Chemical Energetics 

04 March 2024

Example 2:

STEPS:

Step 1 : Draw and label the x and y axes.<div>Step 2 : Write the chemical equation.</div><div>Step 3 : Identify whether it is an exothermic or endothermic reaction.</div><div>Step 4 : Draw the line for the reactant.</div><div>Step 5 : Draw the line for the product.</div><div>Step 6 : Draw the arrow for the energy released or absorbed.</div>

CaCO₃ (s) →  CaO (s) + CO₂ (g)          △H = +178 kJ/mol

heat

Write your team hypothesis or prediction.

Hypothesis

Follow the steps on pages 71 and 72 of your practical workbook.

Experiment Proper

Closing : Lesson Key Points