Chemistry (C5) Flashcards
Which type of reaction releases energy into the surroundings?
Exothermic
Which type of reaction absorbs energy from the surroundings?
Endothermic
In an exothermic reaction, what has more energy in it? The products or the reactants?
Reactants
In an endothermic reaction, what has more energy in it? The products or the reactants?
Products
What would happen to the temperature of the surroundings in an exothermic reaction?
Increase
What would happen to the temperature of the surroundings in an endothermic reaction?
Decrease
Give three examples of endothermic reactions.
Thermal decomposition reactions
Citric acid + sodium hydrogen carbonate
Sports injury packs
Photosynthesis
Give three examples of exothermic reactions.
Combustion
Oxidation
Neutralisation
Displacement
Respiration
Self-heating cans
Hand warmers
What is the unit for temperature?
Degrees Celsius (oC)
Describe how to determine the temperature change of the reaction between hydrochloric acid and sodium hydroxide solutions.
• Put a measured volume of hydrochloric acid and pour into a polystyrene cup with a lid.
• Record the initial temperature using a thermometer.
• Add a measured volume of sodium hydroxide into the beaker and stir, replace lid.
• Record the final temperature of the mixture.
• Calculate the temperature change of the reaction.
Define ‘activation energy’.
Minimum amount of energy that particles must collide with to react.
What is the substance called that reduces the activation energy required by a reaction?
Catalyst
Is energy released when bonds are broken or bonds are made?
Made
Is energy absorbed when bonds are broken or bonds are made?
Broken
Describe an endothermic reaction in terms of bond making and breaking.
More energy is required to break the bonds than is released when bonds are made.
Describe an exothermic reaction in terms of bond making and breaking.
More energy is released when bonds are made than is required to break the bonds.
State how to calculate energy change in a reaction.
Overall energy change = sum of energy required to break bonds – sum of energy released making bonds.
What type of energy change would an exothermic reaction have?
Negative (energy is released)
What type of energy change would an endothermic reaction have?
Positive (energy is taken in)
What is an electrolyte?
A liquid that conducts electricity.
Explain why sodium chloride solution is a good electrolyte.
It contains positive and negative ions that are free to move and carry their charge.
Describe how to make a simple chemical cell.
Connect two pieces of different metals (electrodes) to an electrolyte.
Describe how to make a chemical battery.
Connect two or more chemical cells together in series.
What two factors affect the potential difference (voltage) produced by a chemical cell/battery?
- The metals used as electrodes
- The electrolyte used
Which two metals used in a chemical cell would produce the biggest voltage? Why?
Aluminium and copper
The bigger the difference in reactivity, the bigger the voltage produced.
What is the chemical difference between a rechargeable and non-rechargeable cell?
Renewable cells - chemical reaction reversed by an external electrical current.
Non-rechargeable cells/batteries work until…
One of the reactants is used up.
Which type of reaction occurs in a rechargeable cell?
Reversible.
Which type of battery is more expensive initially? Rechargeable or non-rechargeable?
Rechargeable.
Which type of battery is more expensive in the long term?
Non-rechargeable.
What is the name of the fuel cell in which hydrogen is oxidised to produce water and energy?
Hydrogen fuel cell.
What is the word equation for the reaction taking place in a hydrogen fuel cell?
Hydrogen + oxygen → water.
Suggest two advantages of using hydrogen fuel cells over rechargeable batteries.
• The only waste product of hydrogen fuel cells is water.
• Keep producing electricity as long as fuel is provided.
Suggest two disadvantages of using hydrogen fuel cells over rechargeable batteries.
• They are very expensive.
• Difficult to transport and store hydrogen as it is a flammable gas.
• Most hydrogen comes from methane in natural gas (fossil fuel).
What is the half equation for the reaction at the cathode in a hydrogen fuel cell? Is this oxidation or reduction?
O2 + 4H+ + 4e- → 2H2O
Reduction.
What is the half equation for the reaction of hydrogen at the anode in a hydrogen fuel cell? Is this oxidation or reduction?
2H2 → 4H+ + 4e-
Oxidation.
