Energy Changes Flashcards
(22 cards)
In an exothermic reaction is heat transferred to or from the surroundings
To the surroundings
Name two different types of reaction which are exothermic
- Combustion
- Neutralisation
Define what is meant by an endothermic reaction
An endothermic reaction is one which takes in energy from the surroundings.
Write down the equation for the thermal decomposition of calcium carbonate
CaCO3 (+heat) –> CO2 + CaO
What is the purpose of putting the reaction container into a beaker containing cotton wool during an experiment to investigate the temperature change of an exothermic reaction
To provide insulation so that energy is not lost to the surroundings
What is the activation energy of a reaction
The minimum amount of energy the reactants need to collide with each other and react.
In an endothermic reaction do the products of the reaction have more or less energy than the reactants
The products have more energy than the reactants
What type of process is bond breaking
Endothermic
What type of process is bond forming
Exothermic
In what type of reaction is the energy released by forming bonds greater than the energy used to break them
Exothermic
What three steps would you use to find the overall energy change in a reaction if you were given the known bond enthalpies for the bonds present in the reactants and products
- Find the energy required to break the original bonds
- Find the energy released by forming the new bonds
- Find the overall energy change by subtracting energy released by forming bonds by energy required to break bonds
What is an electrolyte in an electrochemical cell
A liquid that contains ions which react with the electodes
Give two factors that affect the voltage produced by an electrochemical cell
- Types of electrodes used, the bigger the difference in reactivity of electrodes the bigger the voltage of the cell
- THe electrolyte used in a cell as different ions in solution will react differently with the metal electrodes used
What is a battery
Formed by connecting two or more cells together in series. The voltages of the cells in the battery are combined so there is a bigger voltage overall.
Explain why non-rechargeable batteries eventually lose their charge
In some cells the chemical reactions that happen at the electrodes are irreversible so over time the reacting particles get used up therefore the reaction can’t happen
What is a fuel cell
An electrical cell that’s supplied with a fuel and oxygen and uses energy from the reaction between them to produce electrical energy
Name an electrolyte commonly used in hydrogen oxygen fuel cells
Potassium hydroxide
In a hydrogen oxygen fuel cell which molecule becomes oxidised and which becomes reduced
Hydrogen loses electrons to produce H+ ions and becomes oxidised
Oxygen gains electrons from the cathode and reacts with H+ ions to make water, it gets reduced
Write down the overall equation for the reaction in hydrogen oxygen fuel cells
2H2 + O2 –> 2H2O
Why is the reaction that takes place in a hydrogen oxygen fuel cell described as a redox reaction
Because there is reduction at the cathode an oxidation at the anode
State 3 advantages of hydrogen oxygen fuel cell powered cars over battery powered electrical cars
- Don’t produced as many pollutants as batteries are more polluting to dispose off
- There is a limit to how many times batteries can be recharged.
- Batteries store less energy than fuel cells
- Batteries are more expensive to make than fuel cells
Describe how a hydrogen oxygen fuel cell works
Hydrogen goes into the anode compartment and oxygen goes into the cathode compartment . At the anode hydrogen is oxidised to produce H+ ions and the H+ ions in the electrolyte move to the cathode. At the cathode oxygen is reduced and reacts with H+ ions to make water. The electrons flow through an external circuit from the anode to the cathode, which is the electric current
