energy changes Flashcards
Hydrogen fuel cells can be used to power different forms of transport.
some diesel trains are being converted to run on hydrogen fuel cells .
A newspaper article referred to the newly converted trains as “steam trains”
suggest why
hydrogen is oxidised to produced water .
water is released as steam
The reaction between hydrogen and oxygen in a hydrogen fuel cell is used
to produce electricity.
Hydrogen fuel cells and rechargeable cells are used to power some cars.
Give two advantages of using hydrogen fuel cells instead of using
rechargeable cells to power cars.
takes less time to refuel than rechargable cells
no loss of effieciency over time
what is an exothermic reaction
when energy is transferred or released to the surroundings
give examples/types of exothermic reactions
neutralisation reactions
oxidation reactins
combustion
describe how the products and reactants are in the energy profile of an exothermic reaction
reactants have more enegy and so they are palced higher in the energy profile diagram
products have less energy, so they are placed beneath the reactants in the energy profile diagram
what is an endothermic reaction
when enegy is taken in from the surroundings
give examples of endothermic reactions
thermal decomposition
describe how the products and reactants are in the energy profile of an endothermic reaction
reactants have less energy and are benaeth the products in the energy profile diagram
products have more energy and are above the reactants in the energy profile diagram
what is the temperature for an exothermic reaction
temp rises - hot
what is temperature for an endothermic reaction
temp falls - cold
what is activation energy
minimum amount of energy needed for the reaction to happen
how would you know that the reaction is exothermic when using bond energies to calculate the overall energy change
the energy used to break the bond is less than the enrgy used to make the bond
so the overall enegy change would be shown with a negative sign
how would you know that the reaction is endothermic when using bond energies to calculate the overall energy change
the energy used to break the bonds is greater than the energy used to make the bonds, so the overall change can be shown with a positive sign
what type of reaction is breaking a bond
endothermic
what type of reaction is making a bond
exothermic
describe the method of investigating temperature change in chemical reactions
1.Measure 30 cm³ of dilute hydrochloric acid using a measuring cylinder
2. Transfer the acid into a polystyrene cup that’s inside a beaker
3. Measure the initial temp of the acid and record
4. Measure 5 cm³ of sodium hydroxide solution using a measuring cylinder.
5. Transfer the sodium hydroxide solution to the polystyrene cup that has the hydrochloric acid.
6. Gently stir the solution with the thermometer.
7. Record the highest temperature reached when the reading stops changing.
8. Rinse out the polystyrene cup.
9. Repeat the experiment with increasing volumes of sodium hydroxide solution (in increments of 5 cm³) up to a maximum of 40 cm³.
10. Repeat the entire experiment to obtain two sets of results and calculate a mean value for the maximum temperature reached for each volume of sodium hydroxide solution.
Give results from the chemical reaction of adding NaOH in increments of 5cm3 to the hydrcloric acid
As the volume of sodium hydroxide increases, the maximum temperature reached increases
At a certain volume, the maximum temperature reached starts to decrease.
why is it that adding more sodium hydroxide doesn’t lead to a further increase in temperature, and it starts to decrease
- There is not enough hydrochloric acid to react with all the added sodium hydroxide.
(making HCL the limiting reactant and the NaOH in excess)
2.The energy released is spread out into a greater volume of solution
what is the purpose of the polysterene cup with the lid when investigating temperature change
Polystyrene is a good thermal insulator, so it reduces heat loss through the sides and bottom of the container. The lid reduces heat loss to the air.
what is a cell in the context of these “energy changes topic”
A cell is a setup where a chemical reaction takes place on the surface of two metals placed in an electrolyte solution, producing electricity.
what happens when two different metals are placed in an electrolyte
produce electricity
what are some cons/disadvantages of cells
Cells only produce electricity for a limited time because the chemicals in the cell eventually run out.
Cells only produce electricity if metals with different reactivity are used.
what does a greater difference in the reactivity of metals imply about the potenetial diffrence produced by the cell
the greater the difference in the reactivity of the metalsthe greater the potential difference produced by the cell.
what is a battery
A battery contains two or more cells connected in series. This produces a greater voltage.
disadvantsge of using non rechargeable/alkaline batteries over rechargeable batteries
Reactants run out, and no more electricity is produced.
The chemical reactions cannot be reversed.
advantage of using rechargable batteries over rechargable batteries
Chemical reactions can be reversed by applying an electrical current.
what is a fuel cell
A fuel cell is a type of cell that generates electricity through a chemical reaction between a fuel, such as hydrogen, and an oxidant, such as oxygen or air.
what is the waste product of hydrogen fuel cells
water
write the half equation for what happens to the hyrogen at the negative electrode (anode)
2H2 →4H+ +4e −
write the half equation for what happens to the oxygen at the positive electrode (cathode)
.
O2+4H+ +4e−→2H2O
what is the overall equation for the reaction in a hydrogen fuel cell
2H2 + O2 → 2H2O
Advantages of Hydrogen Fuel Cells over rechargable batteries
Produce electricity as long as hydrogen is supplied.
Do not become less efficient over time.
Can be a source of drinking water (e.g., for astronauts).
Disadvantages of Hydrogen Fuel Cells
Use hydrogen, which is an explosive and difficult-to-store gas.
Produce a relatively low voltage, requiring several cells to be connected.
disadvantages of rechargable batteries
1.rechargable batteries run out and need to be recharged
2. they can store less electricity the more charging cycles they go through and eventually need to be replaced
advantages of rechargable batteries over hydrogen fuel cell
no dangerous fuels are rquired for this reaction
they can produce a greater potential difference
Plan a method to investigate the effect of changing the mass of sodium carbonate
powder on the highest temperature reached.
- measure volume of HCL with a measuring cylinder
- pour HCL into a polysterene cup
- Measure the initial temp of HCL
- add a known mass of sodium carbonate, measured with a balance
- stir
- measure the highest temp reached.
- add successive masses of sodium carbonate to the same mixture
- repeat the whole investigation
