Topic 5 - Energy Changes Flashcards
Does the overall amount of energy in a reaction change?
No because energy is conserved. It cant be created or destroyed.
What is an exothermic reaction? Give some examples and how theyre used in everyday life.
A reaction that transfers heat to surroundings. (Heat is lost).
Best example is burning fuels (combustion).
Neutralisation reactions are also exothermic.
Oxidation reactions.
Used for hand warmers.
Self heating cans.
What is an endothermic reaction? Give some examples and how theyre used in everyday life.
A reaction which takes in energy from surroundings.
Less common but some examples are
Reaction between citric acid and sodium hydrogencarbonate
Thermal decomposition
Used for sports injury packs. Becomes instantly cool.
Whats a reaction profile?
Diagrams that show relative energies of reactants and products in a reaction.
What is activation energy?
Minimum amount of energy needed for reactants to collide with each other and react.
Is bond breaking endothermic or exothermic? And bond forming?
Bond breaking is endothermic. (Energy is supplied)
Bond forming is exothermic. (Energy is released)
What is an electrochemical cell?
A basic system made up of 2 different electrodes in contact with an electrolyte
What does the voltage of an electrochemical cell depend on?
Type of metal - the bigger the difference in reactivity between the metals, the bigger the voltage.
The electrolyte
How is a battery formed?
Connecting 2 or more electrochemical cells together in series.
Why are some batteries non rechargeable?
Non rechargeable batteries contain cells which use irreversible reactions. Once one of the reactants is used up, they dont produce anymore charge.
What is a fuel cell?
A fuel cell is an electrical cell thats supplied with a fuel and oxygen and uses energy from the reaction between them to produce electrical energy.
How do fuel cells work?
When fuel enters the cell it becomes oxidised and sets up a potential difference within the cell.
Give an example of a fuel cell
Hydrogen-oxygen fuel cell
How does a hydrogen oxygen fuel cell work?
Electrolyte is often potassium hydroxide.
Hydrogen reacts at anode and loses electrons to form H+ ions. (Oxidation). The H+ ions move through the electrolyte to the cathode.
At cathode oxygen gains electrons and reacts with H+ ions in electrolyte to form water. (Reduction).
Electrons flow through external circuit from the anode to cathode. This is the electric current.
What are hydrogen oxygen fuel cells used for?
Electric vehicles
Batteries
