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Questions and Answers
Which of the following are examples of exothermic reactions?
Which of the following are examples of exothermic reactions?
Endothermic reactions involve the transfer of energy from the reacting chemicals to the surroundings.
Endothermic reactions involve the transfer of energy from the reacting chemicals to the surroundings.
False
The energy change (ΔΗ) in an exothermic reaction is positive.
The energy change (ΔΗ) in an exothermic reaction is positive.
False
In an exothermic reaction, the reactants are at a lower energy level than the products.
In an exothermic reaction, the reactants are at a lower energy level than the products.
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What is the minimum amount of energy required for a chemical reaction to take place?
What is the minimum amount of energy required for a chemical reaction to take place?
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What is the name of the alternative pathway for a chemical reaction that catalysts provide?
What is the name of the alternative pathway for a chemical reaction that catalysts provide?
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What is the unit used to measure bond energies?
What is the unit used to measure bond energies?
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Study Notes
Exothermic and Endothermic Reactions
- Exothermic reactions release energy to the surroundings, increasing temperature. Examples include combustion, respiration, and neutralisation.
- Endothermic reactions absorb energy from the surroundings, decreasing temperature. Examples include thermal decomposition of calcium carbonate and dissolving sherbet.
Reaction Profiles
- Exothermic: Reactants have higher energy than products; energy is released to the surroundings.
- Endothermic: Reactants have lower energy than products; energy is absorbed from the surroundings.
Activation Energy
- Activation energy is the minimum energy needed for a reaction to start.
- Catalysts lower activation energy, speeding up reactions.
Bond Making and Bond Breaking
- Bond breaking requires energy (endothermic).
- Bond making releases energy (exothermic).
- Energy changes in reactions are measured in kJ/mol.
Calculations Using Bond Energies
- Bond energies are used to calculate the overall energy change in a reaction.
- Total bond energy of broken bonds minus total bond energy of created bonds = overall energy change.
- Negative value indicates an exothermic reaction, positive value indicates an endothermic reaction.
Required Practical: Investigating Variables Affecting Temperature Changes
- Aim: Investigate how different variables affect the temperature changes in reactions (e.g., acid + metal, acid + carbonate, neutralisation).
- Equipment: Polystyrene cup, measuring cylinder, thermometer, beaker, balance.
- Method: Control variables (acid concentration), measure starting temperature, add reactants, measure temperature change.
Chemical Cells
- Chemical cells convert chemical energy to electrical energy.
- Rechargeable cells can be recharged; non-rechargeable cells cannot.
- Voltage depends on the reactivity difference between metals in the cell.
Fuel Cells
- Fuel cells produce electricity continuously by reacting a fuel (like hydrogen) with oxygen.
- The only product is water.
- This process is a redox reaction, where oxidation and reduction happen simultaneously.
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Description
Test your knowledge on exothermic and endothermic reactions with this engaging quiz. Explore the concepts of energy release, activation energy, and the role of catalysts in chemical reactions. Dive into the intricacies of bond making and breaking, along with calculations using bond energies.
