C5 Energy Changes Flashcards
(12 cards)
Activation energy
Minimum amount of energy needed for particles to react
What occurs with energy when bonds are broken or formed
Bonds broken-Takes in energy in form of heat
Bonds formed-Releases energy in form of heat
Draw the reaction profile for an exothermic reaction
Reactants higher than products.
Small arrow up for activation energy.
Large arrow down shows overall energy loss.
Draw the reaction profile for an endothermic reaction
Reactants lower than prodcuts.
Activation energy long arrow just above products.
Energy absorbed goes up to products
Exothermic
Endothermic
Exothermic-A reaction which transfers energy to surroundings usually in the form of heat.
Endothermic-A reaction in which it takes in energy from the surroundings. Shown by a fall temperature.
2 examples of endothermic/Exothermic reactions
Endothermic- Citric acid+ Sodium hydrogencarbonate
Thermal decomposition
Exothermic-Combustion
Neutrilisation
Definition
Fuel cell
An electrical cell that supplied with a fuel and oxygen
How does a fuel cell work
The electrolyte is often an acid and the electrodes are often pouros carbon with a catalyst.
Hydrogen enters the anode(pos) compartment.
Oxygen enters cathode(neg) compartment
At the anode. Hydrogen loses electrons to produce H+ ions. This is oxidation.
H+ ions in electrolyte move to the cathode
At the cathode oxygen gains electrons from cathode and reacts with H+ ions to make water. This is called reduction.
Electrons flow through an external circuit from anode to the cathode. This is the electric current.
Overall reaction is hydrogen plus oxygen which gives water.
3 Advantage/Disadvantages of fuel cells
Pros-Not many pollutants
Fuel cells store more energy than batteries
Fuel cells are easier to dispose of compared to batteries as they contain heavy metals
Cons-Hydrogen is a gas so takes up more space to store than battery
Explosive when mixed with air so hard to store
Hydrogen fuel is either made from hydrocarbons or electroloysis which uses electricity or fossil fuels
Describe an electrochemical cell
Made of 2 electrodes placed in electrolyte.
Electrodes are made of metal
Electrodes are connected by a wire so that cahrge can flow between them
Voltmeter is used to measure the charge within the cell.
Why are alkaline batteries non-rechargeable
Contain cells that use irreversible reactions meaning that ions are fully used up during the reaction
Required Practical
Describe how to measure temperature change
Measure 25cm^3 of acid into polystyrene cup
Stand cup into beaker making cup more stable
Measure and record temperature of acid using thermometer
Measure 5cm^3 of alkali and add it to the polystyrene cup.
Put lid on the cup and gently stir the solution with the thermometer through the hole in lid
When the reading of the thermometer stops changing record the temperature.
Repeat steps 4 and 5 to add further 5cm^3 of the alkali to the cup
Then calculate mean maximum temperature
