C1- Energy Changes Flashcards
What does exothermic mean?
Heat is given out
What does endothermic mean?
Heat is taken in
How is energy moved around in chemical reactions?
Different chemicals store different amounts of energy, if the reaction products store more energy than the original reactants they must have taken in energy from their surroundings. If less, the excess was transferred to the surroundings. The overall amount is the same because energy cannot be created or destroyed.
Give 3 examples of an exothermic reaction
Combustion which is the burning of fuels
Neutralisation reactions
Oxidation reactions
Give 3 examples of an endothermic reaction
Reaction between Citric Acid and Sodium Hydrogen carbonate
Thermal decomposition
Cooling Packs
What do reaction profiles show?
Energy changes
Exothermic reaction profile
In book
Endothermic reaction profile
In book
What happens to bonds in a chemical reaction and is it exo or endo?
Old bonds are broken and new ones are formed. Energy must be supplied for bond breaking making it endo. Energy is released during bond formation making it exo.
What is the bond breaking and forming relationship in endothermic and exothermic reactions?
In endothermic reactions the energy used to break bonds is greater than the energy released and vice versa.
What is an electrochemical cell?
A basic system made up of two different electrodes in contact with an electrolyte
How does an electrochemical cell use chemical reactions to produce electricity?
- The two electrodes must be able to conduct electricity so are usually metals
- The electrolyte is a liquid that contains ions which react with the electrodes
- The chemical reactions between the electrodes and the electrolyte set up a charge difference between the electrodes
- If the electrodes are then connected by a wire, the charge is able to flow and electricity is produced
- A voltmeter can also be connected to the circuit to measure the voltage of the cell
What does using different metals (type of electrodes) to react with the same electrolyte cause?
Charge difference or voltage of the cell
How does a bigger difference in reactivity of electrodes affect the voltage of the cell?
Causes a bigger voltage of the cell
How does the electrolyte used in a cell affect the voltage size?
Different ions in the solution will react differently with different metal electrons
How do you form a battery using cells and how does it affect the voltage?
A battery is formed by connecting 2 or more cells together in series, the voltage of the cells is combined causing a larger overall voltage
What happens to reactants in non rechargeable batteries?
They are used up
Why do reactants get used up in non rechargeable batteries?
In some cells the chemical reactions at the electrodes are irreversible, as overtime the reactants get used up and turned into products, when any one of the reactants is used up the reaction can no longer happen and no electricity is produced
How can a reaction be reversed in a rechargeable cell?
By connecting the cell to an external electric current
What is a fuel cell and what does it produce?
An electrical cell that is supplied with a fuel and oxygen and uses energy from the reaction between them to produce electrical energy efficiently
How does a fuel cell work?
When the fuel enters the cell, it becomes oxidised and sets up a potential difference within the cell
What is a good example of a fuel cell?
A hydrogen oxygen fuel cell produces clean water and releases energy
What type of reaction does a hydrogen fuel cell involve?
A redox reaction
Which electrodes do hydrogen and oxygen go into respectively?
Anode and cathode
What could hydrogen fuel cells be used in?
Vehicles
Other than hydrogen fuel cells, what is another renewable energy source for cars?
Electrical batteries
What are the benefits of using hydrogen fuel cells for vehicles?
- They don’t produce as many pollutants, only by products are water and heat
- Less polluting to dispose of than electric batteries which are made of highly toxic metal compounds
- Batteries are more expensive and can only be recharged so many times before they need to be replaced and they need to be recharged more often
What are the disadvantages of using hydrogen fuel cells
- Hydrogen is a gas so it takes a lot more space to store than a battery
- Hydrogen is explosive when mixed with air so it’s hard to store it safely
- The hydrogen is often made from hydrocarbons (from fossil fuels) or electrolysis of water which uses electricity (usually generated by fossil fuels)
