C5 Flashcards
What is activation energy?
The minimum amount of energy for particles to collide into each other for a successful reaction to happen
What is a feature of alkaline batteries?
They are non rechargeable. In non rechargeable cells and batteries this means the chemical reactions stop when one of the reactants have been used up
What are batteries?
Two or more cells that are connected together in series to provide a greater voltage
What are chemical cells?
Cells that contain chemicals that react to produce electricity
What is an endothermic reaction?
Takes the energy in from the surroundings so the temperature in the surroundings decrease (can be seen by a decrease in temp in the thermometer). IN ENDOTHERMIC REACTIONS, THE ENERGY REQUIRED TO BREAK THE EXISTING BONDS IS GREATER THAN THE ENERGY RELEASED FROM FORMING NEW BONDS
What is an exothermic reaction?
The energy is transferred into the surroundings so the temperature around increases (can be seen by an increase in temp in the thermometer). IN AN EXOTHERMIC REACTION, THE ENERGY RELEASED FROM FORMING NEW BONDS IS GREATER THAN THE ENERGY NEEDED TO BREAK EXISTING BONDS
What are fuel cells?
Cells that are supplied by an external source of fuel (e.g. hydrogen) and oxygen or air. The fuel is then oxidised within the fuel cell to create potential difference
What is the equation for the overall energy change?
Difference between the sum of the energy needed to break bonds and the sum of the energy released when bonds in the products are formed
What is a reaction profile?
A graph that shows the relative energies of the reactants and products, the activation energy and the overall energy change of a reaction.
What is a rechargeable cell?
They are rechargeable, and this is because the chemical reactions are reversed when an external electric current is supplied
What are examples of an exothermic reaction?
Neutralisation, combustion and respiration
What are examples of an exothermic reaction?
Neutralisation, combustion and respiration
What are examples of endothermic reactions?
Photosynthesis, ice packs, thermal decomposition
What is the overall energy change?
The difference between the energy needed to break the bonds and the energy released when making them
What is the overall energy change?
The difference between the energy needed to break the bonds and the energy released when making them
Which is exothermic and which is endothermic- bond breaking and bond making?
Bond MAKING is exothermic
Bond BREAKING is endothermic
Where does oxidation and reduction occur?
Oxidation always occurs at the anode
Reduction always occurs at the cathode
What are advantages of hydrogen fuel cells?
No pollution
Quick to refuel
Powerful enough so lorries can use them
What are the disadvantages of using hydrogen fuel cells?
Hydrogen is an explosive gas
Very expensive
Hard to store the gas
What are biological catalysts?
It speeds up the rate of reaction
It doesn’t get used up itself
Catalysts provide a different pathway that has a lower activation energy
