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What is the method to investigate energy changes?
Place a polystyrene cup inside a beaker to provide stability.
Measure a set volume (e.g., 25 cm³) of hydrochloric acid using a measuring cylinder. Pour it into the polystyrene cup.
Record the initial temperature of the acid using a thermometer.
Measure a set volume of sodium hydroxide solution (e.g., 25 cm³).
Add the sodium hydroxide solution to the acid in the cup. Quickly place the lid on the cup and insert the thermometer through the lid.
Stir the solution gently and record the maximum temperature reached.
Repeat the experiment with different concentrations of acid or base.
Calculate the temperature change for each reaction and compare results.
What is the aim of this practical?
To investigate temperature changes during exothermic and endothermic reactions.
Why is a polystyrene cup used in this experiment?
To reduce heat loss to the surroundings.
What reaction is being studied in this practical?
Neutralization between hydrochloric acid and sodium hydroxide.
How is the initial temperature measured?
Using a thermometer before adding the second solution.
Why is the lid placed on the polystyrene cup?
To minimize heat loss to the environment.
What is the role of the stirring rod?
To ensure the solutions mix evenly.
What type of reaction occurs when acid reacts with an alkali?
Exothermic reaction.
Why is a beaker placed around the polystyrene cup?
To provide stability and prevent spills.
How do you calculate the temperature change?
Subtract the initial temperature from the maximum temperature.
Why are different concentrations of acid or base used in repeats?
To investigate how concentration affects the temperature change.
What is an example of an exothermic reaction observed in this practical?
Neutralization of HCl and NaOH.
How can the experiment be modified to investigate an endothermic reaction?
Use chemicals that absorb heat, e.g., dissolving ammonium nitrate in water.
Why is it important to stir the mixture?
To ensure uniform temperature distribution.
What safety precautions should be taken during this practical?
Wear goggles and gloves, and handle acids and alkalis carefully.
How could the accuracy of this experiment be improved?
Use a digital thermometer or repeat trials for consistency.
What is a fuel cell?
A cell that produces electricity by reacting a fuel with oxygen.
Give an example of a fuel used in fuel cells.
Hydrogen.
What is the main product of a hydrogen fuel cell?
Water.
Write the overall equation for a hydrogen fuel cell.
2H2+O2→2H2O
What are the two electrodes in a hydrogen fuel cell?
Anode (hydrogen) and cathode (oxygen).
What type of reaction occurs in a fuel cell?
Redox reactions.
What are the advantages of fuel cells?
They are efficient, produce no pollutants, and are renewable.
What are the disadvantages of fuel cells?
Hydrogen storage is difficult and expensive.
Why are fuel cells considered environmentally friendly?
They produce only water and no greenhouse gases.
What is the role of the electrolyte in a fuel cell?
It allows ions to move between the electrodes.
Why is hydrogen used as a fuel in fuel cells?
It is highly reactive and produces a high energy output.
What is the energy efficiency of a fuel cell compared to a combustion engine?
Fuel cells are more efficient.
Why are fuel cells used in spacecraft?
They provide water as a byproduct and are reliable.
What is the half-equation for hydrogen oxidation in a fuel cell?
2H2→4H++4e−
What is the half-equation for oxygen reduction in a fuel cell?
O2+4H++4e−→2H2O
What is a chemical cell?
A device that produces electricity from a chemical reaction.
What is a battery?
Two or more chemical cells connected in series.
How does a chemical cell work?
By transferring electrons in a redox reaction.
What type of reaction occurs in a cell?
Redox reactions.
What is the role of an electrolyte in a cell?
It allows ions to move and conduct electricity.
Why does a cell stop producing electricity?
The reactants are used up.
What determines the voltage of a cell?
The difference in reactivity of the electrodes.
Why do non-rechargeable batteries eventually stop working?
The chemical reactions are irreversible.
Name a common rechargeable battery.
Lithium-ion battery.
What is the advantage of rechargeable batteries?
They can be reused multiple times.
What is the disadvantage of non-rechargeable batteries?
They contribute to waste and environmental pollution.
Write a redox reaction that occurs in a cell.
Zn+Cu2+→Zn2++Cu
Why are alkaline batteries better than traditional ones?
They last longer and provide more energy.
What is the role of the electrodes in a cell?
To conduct electricity and participate in redox reactions.
How does connecting cells in series affect the voltage?
The voltages add up.
What are bond energies?
The amount of energy required to break a bond or released when a bond is formed.
Is bond breaking exothermic or endothermic?
Endothermic, as energy is absorbed.
Is bond formation exothermic or endothermic?
Exothermic, as energy is released.
What does a negative energy change indicate?
The reaction is exothermic.
What does a positive energy change indicate?
The reaction is endothermic.
How do you calculate the energy change of a reaction?
Energy to break bonds - Energy to form bonds.
Why is energy needed to break bonds?
To overcome the forces holding atoms together.
Why is energy released when bonds form?
Atoms become more stable, releasing excess energy.
What does a high bond energy indicate about a bond?
It is strong and requires more energy to break.
Give an example of a reaction with a high energy release.
Combustion of methane.
What happens if bond breaking energy exceeds bond forming energy?
The reaction is endothermic.
What happens if bond forming energy exceeds bond breaking energy?
The reaction is exothermic.
Why are bond energies averages?
Bond strengths vary slightly in different molecules.
What unit is used for bond energies?
Kilojoules per mole (kJ/mol).
Why are bond energies important in energy calculations?
They help predict whether a reaction absorbs or releases energy.
What is an endothermic reaction?
A reaction that absorbs energy from the surroundings.
Give an example of an endothermic reaction.
Photosynthesis.
How can you tell a reaction is endothermic?
The temperature of the surroundings decreases.
Write the word equation for photosynthesis.
Carbon dioxide + Water → Glucose + Oxygen
Why are endothermic reactions less common in everyday life?
They require energy input to proceed.
What happens to bonds during an endothermic reaction?
Bonds are broken, requiring energy.
Is the boiling of water endothermic or exothermic?
Endothermic, as it absorbs heat.
How is energy transferred in an endothermic reaction?
From the surroundings to the system.
Why does the temperature decrease during an endothermic reaction?
More energy is absorbed than released.
What type of reaction occurs in ice packs?
Endothermic reaction, absorbing heat.
Is the melting of ice endothermic or exothermic?
Endothermic.
Write a chemical equation for an endothermic reaction.
6CO2+6H2O→C6H12O6+6O2
What type of reaction occurs during thermal decomposition?
Endothermic
Why do endothermic reactions often feel cold?
They absorb heat from their surroundings.
How is energy supplied in an endothermic reaction?
By heat, light, or electricity.
What is an exothermic reaction?
A reaction that releases energy to the surroundings, usually as heat.
Give an example of an exothermic reaction.
Combustion of fuels.
How can you tell a reaction is exothermic?
The temperature of the surroundings increases.
Write the word equation for the combustion of methane.
Methane + Oxygen → Carbon dioxide + Water
Why are exothermic reactions useful in everyday life?
They provide energy, e.g., for heating or powering engines.
Is respiration exothermic or endothermic?
Exothermic, as it releases energy.
What happens to bonds during an exothermic reaction?
Bonds are formed, releasing energy.
How is energy transferred in an exothermic reaction?
To the surroundings as heat.
Why does the temperature increase during an exothermic reaction?
More energy is released than absorbed.
What type of reaction occurs in hand warmers?
Exothermic reaction, often the oxidation of iron.
Is the neutralization of an acid and an alkali exothermic or endothermic?
Exothermic.
Write a chemical equation for an exothermic reaction.
2H2+O2→2H2O+energy
Why are fuels considered exothermic?
Their combustion releases large amounts of energy.
What type of reaction occurs when water freezes?
Exothermic, as energy is released to the surroundings.
What is the role of exothermic reactions in energy production?
They are used to generate heat or electricity.