energy changes Flashcards
What is an exothermic reaction?
A reaction that transfers energy to the surroundings, so the temperature of the surroundings increases
Examples include combustion and neutralisation.
What are examples of exothermic reactions?
- Combustion
- Neutralisation
These reactions release energy in the form of heat.
What are some everyday uses of exothermic reactions?
- Self-heating cans
- Hand warmers
These products utilize the heat generated from exothermic reactions.
What is an endothermic reaction?
A reaction that takes in energy from the surroundings, so the temperature of the surroundings decreases
Examples include thermal decomposition and photosynthesis.
What are some examples of endothermic reactions?
- Thermal decomposition
- Photosynthesis
These reactions absorb heat from their environment.
What are some everyday uses of endothermic reactions?
- Ice packs
- Instant cold packs
These products provide cooling effects through endothermic processes.
What does the reaction profile of an exothermic reaction look like?
The energy of the reactants is higher than that of the products
What does the reaction profile of an endothermic reaction look like?
The energy of the reactants is lower than that of the products
What is the activation energy?
The minimum amount of energy needed for a chemical reaction to take place
What happens to bonds during exothermic reactions?
Bonds are made
What happens to bonds during endothermic reactions?
Bonds are broken
In what type of reactions is the bond energy negative?
Exothermic
In what type of reactions is the bond energy positive?
Endothermic
Taking two different metals and placing them into an electrolyte produces electricity. What is an electrolyte?
A solution that can conduct electricity (e.g., an aqueous solution of an ionic compound)
Why can cells only produce electricity for a certain amount of time?
Because the chemicals in the cell eventually run out and the reaction stops
Cells only produce electricity if metals with different reactivities are used. What is the relationship between reactivity and potential difference?
The larger the difference in reactivities, the larger the potential difference
What is a battery?
Two or more cells connected in series to produce a greater voltage
What 3 factors affect the potential difference?
- The difference in reactivity between the two metals
- The electrolyte
- The amount of cells in the battery
How are rechargeable batteries recharged?
The chemical reactions are reversed when an electrical current is applied
How do hydrogen fuel cells work?
Hydrogen gas is supplied to a negative electrode, which diffuses through the electrode and reacts with hydroxide ions to form water to provide electrons to an external circuit.
Oxygen is supplied to a positive electrode, which diffuses through the graphite and accepts the electrons from the external circuit.
What are the advantages of hydrogen fuel cells?
- They produce electricity for as long as hydrogen is provided
- Don’t get less efficient the more they run
- No pollutants are produced; the only waste product is water
- They can be a range of sizes for different uses
What are disadvantages of hydrogen fuel cells?
- Hydrogen is highly flammable
- Hydrogen is difficult to store
- Hydrogen is sometimes produced for the cell by non-renewable sources
What are advantages of rechargeable batteries?
- They produce a greater voltage than hydrogen fuel cells
- No dangerous fuels are required
What are disadvantages of rechargeable batteries?
- They run out and need to be recharged
- They store less electricity the more they’re charged and eventually need to be replaced
