Topic 5 - Energy Changes Flashcards
Are neutralisation reactions exo or endothermic?
exothermic
Is thermal decomposition endo or exothermic?
endothermic
how can we test the effect of acid concentration on the energy released in a neutralisation reaction?
1.Put 25cm^3 of 0.25mol/dm^3 acid and alkali in separate beakers
2.Place the beakers in a water bath set to 25 degrees until they are both at 25 degrees
3.Add acid followed by the alkali into a polystyrene cup with a lid
4.Take the temperature of the mixture every 30 seconds, and record the highest temp
5.Repeat the previous steps for 0.5mol/dm^3 and 1 mol/dm^3 of acid
What is activation energy?
the minimum energy required for a reaction to take place between reacting particles
What is an electrochemical cell made up of?
2 electrodes in contact with an electrolyte
What is an electrolyte?
an ionic compound that is molten or dissolved in water that conducts electricity and is decomposed by it
How do electrochemical cells work?
- The chemical reactions between the electrodes and the elctrolyte set up a charge difference between the electrodes
- When the electrodes are connected by a wire, the charge is a ble to flow and electricity is producce
What can affect the voltage of an electrochemical cell?
- The type of electrode
- The difference in reactivity between the electrodes
- The electrolyte used in a cell
What is a battery?
A series of two or more cells, where the voltages of the cells are combined
What is the difference in reactions between a rechargable and non-rechargable cell
The reaction in a rechargable battery is reversible by connecting it to an external electric current, while the reaction in a non-rechargable is irreversible
What is a fuel cell?
an electrical cell that uses fuel and oxygen/air to release energy, which is then used to produce electricity.
How does a fuel cell work?
When the fuel eneters the cell it becomes oxidised and sets up a potential difference within the cell.
What is an example of a fuel cell?
Hydrogen-oxygen fuel cell
How does a hydrogen-oxygen fuel cell work?
- Hydrogen goes into the anode compartment and oxygen goes into the cathode compartment
- At the anode, hydrogen loses electrons and produces H+ ions - oxidation
- H+ ions in the electrolyte move to the cathode
- At the cathode, oxygen gains electrons from the cathode and reacts with H+ ions to make water - reduction
- The electrons flow through an external circuit from the anode to the cathode - this is the current
What is the overall reaction in a hydrogen-oxygen fuel cell?
2H2 + O2 —> 2H2O
Hydrogen + Oxygen —> Water
What is the half equation at the cathode in a hydrogen-oxygen fuel cell?
O2 + 4H+ + 4e- —-> 2H2O
What is the half equation at the anode in a hydrogen-oxygen fuel cell?
H2–> 2H+ + 2e-
What is the difference between the anode/cathode in electrolysis vs fuel cells?
in electrolysis the cathode is negative, and the anode is postive - in fuel cells its opposite, cathode is positive and anode is negative
What are the pros of hydrogen fuel cells?
- don’t produce as many pollutants, only releases water as waste product
- Manufacturing and disposal of a fuel cell is less damaging than electric batteries
- Fuel cells can be refueled indefinitely
- Fuel cells usually last longer per refueling than batteries
What are the cons of hydrogen fuel cells?
- Hydrogen gas is very hard to store
- Hydrogen is explosive when mixed with air
- hydrogen fuel is often made either from hydrocarbons or by electrolysis, both of which require energy from burning fossil fuels potentially
