Exothermic & Endothermic Reactions (AQA GCSE Chemistry)
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Define the term exothermic reaction.
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Define the term exothermic reaction.
An exothermic reaction is a reaction that gives out heat energy to the surroundings causing the temperature of the surroundings to increase.
Define the term endothermic reaction.
An endothermic reaction is a reaction that takes in heat energy from the surroundings causing the temperature of the surroundings to decrease.
True or False?
Neutralisation reactions are exothermic reactions.
True.
Neutralisation reactions are exothermic reactions.
True or False?
Combustion reactions take in energy from the surroundings.
False.
Combustion reactions give out energy to the surroundings
Name the piece of equipment used to measure temperature changes.
The piece of equipment used to measure temperature changes is a thermometer.
True or False?
Temperature will increase in an exothermic reaction.
True.
Temperature will increase in an exothermic reaction.
True or False?
Energy can be created or destroyed in chemical reactions.
False.
Energy cannot be created or destroyed in chemical reactions.
What type of reaction is used in cold packs for sports injuries?
Cold packs for sports injuries use endothermic reactions to take heat away from the recently injured area.
True or False?
If a reaction transfers energy to the surroundings, the products have less energy than the reactants.
True.
If a reaction transfers energy to the surroundings, the products have less energy than the reactants.
What happens to the temperature of the surroundings in an endothermic reaction?
In an endothermic reaction, the temperature of the surroundings decreases as heat energy is absorbed by the system.
Give two uses of exothermic reactions.
Two uses of exothermic reactions are:
Hand warmers
Self-heating cans
Heating
True or False?
The reaction of citric acid and sodium hydrogencarbonate is exothermic.
False.
The reaction of citric acid and sodium hydrogencarbonate is endothermic.
What are reaction profiles?
Reaction profiles are graphical representations of the relative energies of the reactants and products in chemical reactions.
How does a reaction profile show that a reaction is exothermic?
A reaction profile show that a reaction is exothermic because the energy of the products is lower than the energy of the reactants.
True or False?
The difference in height between the energy of reactants and products on an energy level diagram represents the overall energy change of a reaction.
True.
The difference in height between the energy of reactants and products on an energy level diagram represents the overall energy change of a reaction.
How does a reaction profile show that a reaction is endothermic?
An energy level diagram show that a reaction is endothermic because the the energy of the products is higher than the energy of the reactants.
What information is shown on the y-axis of an energy level diagram?
The energy of the reactants and products is displayed on the y-axis of an energy level diagram.
What information is shown on the x-axis of an energy level diagram?
The progress of the reaction is shown on the x-axis of an energy level diagram.
What does an downwards arrow on an energy level diagram indicate?
A downwards arrow on an energy level diagram indicates an exothermic reaction.
What does an upwards arrow on an energy level diagram indicate?
An upwards arrow on an energy level diagram indicates an endothermic reaction.
What does A represent on the reaction profile?
A represents the energy level of the reactants.
What does B represent on the reaction profile?
B represents the progress of the reaction.
What does C represent on the reaction profile?
C represents the overall energy change of the reaction.
What does D represent on the reaction profile?
D represents the activation energy of the reaction.
What type of reaction is shown by the following reaction profile?
The reaction profile shows an exothermic reaction.
What type of reaction is shown in the following reaction profile?
The following reaction profile is for an endothermic reaction.
Define the term activation energy.
Activation energy is the minimum energy colliding particles need in order to react.
Define the term bond energy.
(Higher tier only)
Bond energy is the amount of energy required to break a bond or the amount of energy given out when the bond is formed.
True or False?
Bond breaking is an endothermic process.
(Higher tier only)
True.
Bond breaking is an endothermic process as energy is needed to break bonds, which is absorbed from the reaction surroundings
True or False?
Energy is taken in when bonds are formed.
(Higher tier only)
False.
When new bonds are formed, energy is released which is an exothermic reaction.
True or False?
A reaction is exothermic if more heat energy is released in forming bonds in the products than is required in breaking bonds in the reactants.
(Higher tier only)
True.
A reaction is exothermic if more energy is released when new bonds are formed than what was required to break them.
Explain, in terms of bond making and breaking, why a reaction is endothermic.
(Higher tier only)
A reaction is endothermic because less heat energy is released forming bonds in the products than is required in breaking bonds in the reactants.
Give the three steps involved in calculating the energy change of a reaction using bond energies.
(Higher tier only)
The three steps involved in calculating the enthalpy change using bond energies are:
Calculate the energy required to break bonds
Calculate the energy released when new bonds are formed
Calculate the enthalpy change by taking the energy released away from the energy taken in
True or False?
When calculating the energy required to break bonds and the energy released when new bonds are formed, we do not need to consider the number of moles of the reactant and product.
(Higher tier only)
False.
When calculating the energy required to break bonds and that released when new bonds are formed, we do need to consider the number of moles for each substance. The bond energy is multiplied by the number of moles.
State the equation used to calculate energy change using bond energies.
(Higher tier only)
The equation used to calculate energy change using bond energies is:
energy change = energy taken in - energy given out
Give the unit of energy change.
(Higher tier only)
The unit of energy change is kJ mol-1.
Identify the type and number of each bond being formed in the following reaction:
(Higher tier only)
The type and number of each bond being formed are:
3 C-H bonds
1 C-Cl bond
1 H-Cl bond