What is an exothermic reaction ?

An exothermic reaction is one that transfers thermal energy to the surroundings, causing the temperature of the surroundings to increase.

What is an endothermic reaction ?

An endothermic reaction is one that takes in thermal energy from the surroundings, causing the temperature of the surroundings to decrease.

In an exothermic reaction, thermal energy is transferred from the .......... to the .......... and the temperature of the surroundings increases .

In an exothermic reaction, thermal energy is transferred from the system to the surroundings and the temperature of the surroundings increases .

True or False? Combustion is an example of an endothermic reaction.

False. Combustion is an exothermic reaction. It releases thermal energy to the surroundings, which is why burning substances feel hot.

Give two everyday applications that make use of exothermic reactions.

Two everyday applications that use exothermic reactions: Hand warmers — use exothermic reactions to release heat Self-heating cans of food or drinks — use exothermic reactions to release heat Combustion reactions such as burning fuel in engines are also exothermic.

Why does the temperature of the surroundings decrease during an endothermic reaction?

The reacting system absorbs thermal energy from the surroundings. This energy is used to drive the reaction, so the surroundings lose thermal energy and their temperature drops.

True or False? Cold packs used for sports injuries rely on endothermic reactions.

True. Cold packs contain substances that react endothermically when mixed, absorbing thermal energy from the surroundings (including the injury site), which reduces the temperature.

In an endothermic reaction, the energy change is described as .......... because the system gains energy from the surroundings.

In an endothermic reaction, the energy change is described as positive because the system gains energy from the surroundings.

A reaction mixture rises in temperature from 20°C to 28°C. Is the reaction exothermic or endothermic?

The reaction is exothermic . The temperature of the surroundings has increased, which means thermal energy has been transferred from the reacting system to the surroundings.

Give two examples of endothermic reactions.

Two examples of endothermic reactions: Electrolysis Thermal decomposition The first stages of photosynthesis are also endothermic.

What is activation energy ( E a )? (Extended Tier Only)

Activation energy , E a , is the minimum energy that colliding particles must have in order to react successfully.

On a reaction pathway diagram, where is the activation energy ( E a ) measured from and to? (Extended Tier Only)

E a is measured from the energy level of the reactants up to the highest point on the curve (the transition state). This energy difference represents the minimum energy needed to start the reaction.

On a reaction pathway diagram, the .......... is plotted on the x-axis and .......... is plotted on the y-axis. (Extended Tier Only)

On a reaction pathway diagram, the progress of the reaction is plotted on the x-axis and energy is plotted on the y-axis.

True or False? In an exothermic reaction pathway diagram, the products are shown at a higher energy level than the reactants. (Extended Tier Only)

False. In an exothermic reaction, energy is released to the surroundings, so the products have lower energy than the reactants. The overall energy change Δ H is negative.

How does a reaction pathway diagram for an endothermic reaction differ from one for an exothermic reaction? (Extended Tier Only)

In an endothermic diagram, the products are at a higher energy level than the reactants, so Δ H is positive and the arrow showing the energy change points upwards. In an exothermic diagram, products are lower in energy and Δ H is negative.

The symbol .......... represents the overall enthalpy change of a reaction on a pathway diagram. (Extended Tier Only)

The symbol Δ*H * represents the overall enthalpy change of a reaction on a pathway diagram.

What four features must be labelled on a reaction pathway diagram? (Extended Tier Only)

The four required labels are: reactants , products , the overall enthalpy change Δ*H and the activation energy E a *.

True or False? A reaction with a higher activation energy requires more energy to start than one with a lower activation energy. (Extended Tier Only)

True. Activation energy is the minimum energy colliding particles must have to react. A higher E a means fewer collisions have sufficient energy , so the reaction is harder to start.

What is the sign of Δ H for an exothermic reaction and what does it indicate? (Extended Tier Only)

Δ H is negative for an exothermic reaction. This indicates that the products have less energy than the reactants, so energy has been transferred from the system to the surroundings.

What is enthalpy change (Δ H )? (Extended Tier Only)

Enthalpy change , Δ H , is a measure of the overall heat change of a chemical reaction, representing the difference in energy between products and reactants.

True or False? Bond breaking is an endothermic process. (Extended Tier Only)

True. Bond breaking requires energy to be taken in from the surroundings to overcome the forces holding atoms together. It is therefore an endothermic process.

Bond .......... is an endothermic process and bond .......... is an exothermic process. (Extended Tier Only)

Bond breaking is an endothermic process and bond making is an exothermic process.

Why is bond making an exothermic process? (Extended Tier Only)

When new bonds form, energy is released to the surroundings as the atoms achieve a more stable arrangement. The system loses energy, which is transferred as heat to the surroundings.

What determines whether a reaction is overall exothermic or endothermic in terms of bond energies? (Extended Tier Only)

A reaction is exothermic when more energy is released forming new bonds in the products than is absorbed breaking bonds in the reactants. It is endothermic when more energy is absorbed breaking bonds than is released forming new bonds.

True or False? An endothermic reaction has a negative Δ H value. (Extended Tier Only)

False. An endothermic reaction has a positive Δ H value because the products have more energy than the reactants (the system has gained energy from the surroundings).

If more energy is released during bond .......... than is absorbed during bond .......... , the reaction is exothermic overall. (Extended Tier Only)

If more energy is released during bond making than is absorbed during bond breaking , the reaction is exothermic overall.

What is the sign of Δ H for an endothermic reaction and why? (Extended Tier Only)

Δ H is positive for an endothermic reaction. The products have more energy than the reactants, so the system has gained energy from the surroundings.

How does the energy of the products compare to the reactants in an exothermic reaction? (Extended Tier Only)

In an exothermic reaction, the products have lower energy than the reactants . The difference in energy is released to the surroundings, giving a negative Δ H value.

IGCSEScienceCambridge (CIE)Combined ScienceChemistryFlashcards5. Chemical EnergeticsExothermic & Endothermic Reactions

Exothermic & Endothermic Reactions (Cambridge (CIE) IGCSE Combined Science: Chemistry): Flashcards

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What is an exothermic reaction?

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Cards in this collection (28)

What is an exothermic reaction?
An exothermic reaction is one that transfers thermal energy to the surroundings, causing the temperature of the surroundings to increase.
What is an endothermic reaction?
An endothermic reaction is one that takes in thermal energy from the surroundings, causing the temperature of the surroundings to decrease.
In an exothermic reaction, thermal energy is transferred from the .......... to the .......... and the temperature of the surroundings increases.
In an exothermic reaction, thermal energy is transferred from the system to the surroundings and the temperature of the surroundings increases.
True or False?
Combustion is an example of an endothermic reaction.
False.
Combustion is an exothermic reaction. It releases thermal energy to the surroundings, which is why burning substances feel hot.
Give two everyday applications that make use of exothermic reactions.
Two everyday applications that use exothermic reactions:
1. Hand warmers — use exothermic reactions to release heat
2. Self-heating cans of food or drinks — use exothermic reactions to release heat
Combustion reactions such as burning fuel in engines are also exothermic.
Why does the temperature of the surroundings decrease during an endothermic reaction?
The reacting system absorbs thermal energy from the surroundings. This energy is used to drive the reaction, so the surroundings lose thermal energy and their temperature drops.
True or False?
Cold packs used for sports injuries rely on endothermic reactions.
True.
Cold packs contain substances that react endothermically when mixed, absorbing thermal energy from the surroundings (including the injury site), which reduces the temperature.
In an endothermic reaction, the energy change is described as .......... because the system gains energy from the surroundings.
In an endothermic reaction, the energy change is described as positive because the system gains energy from the surroundings.
A reaction mixture rises in temperature from 20°C to 28°C. Is the reaction exothermic or endothermic?
The reaction is exothermic. The temperature of the surroundings has increased, which means thermal energy has been transferred from the reacting system to the surroundings.
Give two examples of endothermic reactions.
Two examples of endothermic reactions:
1. Electrolysis
2. Thermal decomposition
The first stages of photosynthesis are also endothermic.
What is activation energy (E_a)? (Extended Tier Only)
Activation energy, E_a, is the minimum energy that colliding particles must have in order to react successfully.
On a reaction pathway diagram, where is the activation energy (E_a) measured from and to? (Extended Tier Only)
E_a is measured from the energy level of the reactants up to the highest point on the curve (the transition state). This energy difference represents the minimum energy needed to start the reaction.
On a reaction pathway diagram, the .......... is plotted on the x-axis and .......... is plotted on the y-axis. (Extended Tier Only)
On a reaction pathway diagram, the progress of the reaction is plotted on the x-axis and energy is plotted on the y-axis.
True or False?
In an exothermic reaction pathway diagram, the products are shown at a higher energy level than the reactants. (Extended Tier Only)
False.
In an exothermic reaction, energy is released to the surroundings, so the products have lower energy than the reactants. The overall energy change ΔH is negative.
How does a reaction pathway diagram for an endothermic reaction differ from one for an exothermic reaction? (Extended Tier Only)
In an endothermic diagram, the products are at a higher energy level than the reactants, so ΔH is positive and the arrow showing the energy change points upwards. In an exothermic diagram, products are lower in energy and ΔH is negative.
The symbol .......... represents the overall enthalpy change of a reaction on a pathway diagram. (Extended Tier Only)
The symbol Δ*H* represents the overall enthalpy change of a reaction on a pathway diagram.
What four features must be labelled on a reaction pathway diagram? (Extended Tier Only)
The four required labels are: reactants, products, the overall enthalpy change Δ*H and the activation energy E_a*.
True or False?
A reaction with a higher activation energy requires more energy to start than one with a lower activation energy. (Extended Tier Only)
True.
Activation energy is the minimum energy colliding particles must have to react. A higher E_a means fewer collisions have sufficient energy, so the reaction is harder to start.
What is the sign of ΔH for an exothermic reaction and what does it indicate? (Extended Tier Only)
ΔH is negative for an exothermic reaction. This indicates that the products have less energy than the reactants, so energy has been transferred from the system to the surroundings.
What is enthalpy change (ΔH)? (Extended Tier Only)
Enthalpy change, ΔH, is a measure of the overall heat change of a chemical reaction, representing the difference in energy between products and reactants.
True or False?
Bond breaking is an endothermic process. (Extended Tier Only)
True.
Bond breaking requires energy to be taken in from the surroundings to overcome the forces holding atoms together. It is therefore an endothermic process.
Bond .......... is an endothermic process and bond .......... is an exothermic process. (Extended Tier Only)
Bond breaking is an endothermic process and bond making is an exothermic process.
Why is bond making an exothermic process? (Extended Tier Only)
When new bonds form, energy is released to the surroundings as the atoms achieve a more stable arrangement. The system loses energy, which is transferred as heat to the surroundings.
What determines whether a reaction is overall exothermic or endothermic in terms of bond energies? (Extended Tier Only)
A reaction is exothermic when more energy is released forming new bonds in the products than is absorbed breaking bonds in the reactants. It is endothermic when more energy is absorbed breaking bonds than is released forming new bonds.
True or False?
An endothermic reaction has a negative ΔH value. (Extended Tier Only)
False.
An endothermic reaction has a positive ΔH value because the products have more energy than the reactants (the system has gained energy from the surroundings).
If more energy is released during bond .......... than is absorbed during bond .........., the reaction is exothermic overall. (Extended Tier Only)
If more energy is released during bond making than is absorbed during bond breaking, the reaction is exothermic overall.
What is the sign of ΔH for an endothermic reaction and why? (Extended Tier Only)
ΔH is positive for an endothermic reaction. The products have more energy than the reactants, so the system has gained energy from the surroundings.
How does the energy of the products compare to the reactants in an exothermic reaction? (Extended Tier Only)
In an exothermic reaction, the products have lower energy than the reactants. The difference in energy is released to the surroundings, giving a negative ΔH value.

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