Topic 5 - Energy Changes Flashcards
What is the law of conservation of energy?
Energy is conserved in a reaction. The energy before a chemical reaction is the same as the energy afterwards.
What is an exothermic reaction and an example?
A reaction that transfers energy to the surroundings, combustion
What is an endothermic reaction and an example?
One that takes in energy from the surroundings, thermal decomposition
How do you draw a reaction profile for a exothermic reaction?
Reactants are high up
Products are lower
Activation energy is little higher than reactants
How do you draw a reaction profile for a endothermic reaction?
Reactants low
Products high
Activation energy is large, bigger than product
What two things happen in a chemical reaction?
Energy must be supplied to break bonds in the reactants
Energy is released when bonds in the products are formed
What type of reaction has a negative energy change and why?
An exothermic reaction because the chemicals have lost energy to their surroundings
What type of reaction has a positive energy change?
An endothermic reaction as the chemicals have gained energy from the environment
What is a cell?
They contain chemicals which react to produce electricity
What is a battery?
Two or more cells connected in series together
How can you make a cell?
Place two different metals in an electrolyte
What is a non rechargeable battery?
The chemical reaction will stop when one of the reactants have been used. Alkali batteries are non rechargeable
What is a rechargeable battery?
Batteries that can be recharged because the chemical reactions are reversed when an external electrical current is supplied
How do fuel cells work?
They are supplied by an external fuel and oxygen. The fuel is oxidised electrochemically to produce power
What is the overall reaction is a hydrogen fuel cell?
Hydrogen and oxygen -> water
