P1 - Energy Changes (Done) Flashcards
(28 cards)
What is an exothermic reaction ?
Reaction that gives out energy into the surroundings, due to the fact that products store less energy than the reactants so it’g given out.
What happens because of an exothermic reaction ?
A rise in temperature of the surroundings (like when burning fuels - combustion)
What is an endothermic reaction ?
Reaction that takes in energy from the surroundings, due to the fact that products store more energy than reactants so they take in more during reaction.
What happens because an endothermic reaction ?
A fall in temperature of surroundings (like sports injury packs that become cool instantly).
How can you measure temperature change ?
Record temperature of reactants and mix in polystyrene cup, if temperature rises or falls record the highest/lowest temperature it reaches and take this away from temperature of reactants to find temperature change. If temperature goes up its exothermic, if it goes down it’s endothermic.
What is the problem with measuring temperature change ?
The amount of energy lost to surroundings, which can however be reduced by: putting a lid on the polystyrene cup and putting the cup in a beaker of cotton wool (poor conductor).
What variables does the temperature change of a reaction depend on ?
The mass or concentration of the reactants used.
What reactions could you use in an experiment to measure temperature change ?
Neutralisation reactions, reactions between metals and acids, reactions between acids and carbonates and displacement reactions of metals.
What type of reaction is bond breaking ?
Energy must be supplied to break existing bonds, so it’s an endothermic process.
What type of reaction is bond making ?
Energy is released when new bonds are formed, so it’s an exothermic process.
What are reaction profiles ?
Diagrams that show the relative energies of the reactants and products, and how the energy changes changes over the course of the reaction.
What is the activation energy ?
The minimum amount of energy the reactants need to collide with each other and react.
What is an electrochemical cell ?
A basic system made up of two different electrodes in contact with an electrolyte.
How can an electrochemical cell release energy ?
The chemical reactions between the electrodes and the electrolyte set up a charge difference between the electrodes, if the electrodes are connected by a wire the charge is able to flow and electricity is produced.
What is a battery ?
It’s 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 overall charge.
What affects the voltage of a cell ?
The type of metals used for the electrodes, and also the electrolyte used - as different ions in solution will react differently with the electrodes.
What happens in non-rechargeable batteries ?
The reactants get used up and turn into the products of the reaction, and the reaction can no longer happen so no electricity is produced.
What happens in rechargeable batteries ?
The reaction between the ions and solution and the electrodes can be reversed by connecting it to an external electric current.
What are fuel cells ?
An electrical cell that’s 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 in the cell.
What types of fuel cell are there ?
There are a few different types, using different fuels and electrolytes - one of which is the hydrogen-oxygen fuel cell which produces clean water and energy.
What is the difference between batteries and fuel cells ?
Batteries are much more polluting to dispose of as they’re made with highly toxic metal compounds, batteries in cars are rechargeable but there’s a limit to how many times before they need replacing. Fuel cells store more energy, and produce less pollutants - only water and heat.
What are the components in hydrogen-oxygen fuel cells made of ?
Electrolyte is often an acid - phosphoric acid, but can also be an alkali - potassium hydroxide, and the electrodes are often porous carbon with a catalyst.
What happens inside the hydrogen-oxygen fuel cells ?
Hydrogen goes in the anode compartment and oxygen goes in the cathode compartment. Electrons transferred between the atoms and electrons flow through an external circuit from the anode to the cathode - this is the electric current.
