Unit 5- Energy Changes Flashcards
(15 cards)
What is an Exothermic reaction
One which transfers energy to the surroundings usually by heating. This is shown as a rise in temperature
What is an endothermic reaction
Reactions which takes energy in from the surroundings, this is shown as a fall in temperature
Example of Exothermic reaction
Neutralisation, combustion
Uses of Exothermic reactions
Hand warmers- use the Exothermic oxidation of iron in air to release energy
Self heating cans
Example of endothermic reaction
Thermal decomposition
Uses of endothermic reactions
Used in sport injury packs, allows pack to become instantly cooler without having to be put in freezer
What is a fuel cell
Electrical cell that produces electricity using fuel and oxygen
Uses of fuel cells
Used in vehicles- don’t produce nasty pollutants, however uses a lot of energy
What is the voltage in a cell dependant on
Type of electrode and electrolyte
Advantages and disadvantages of hydrogen fuel cells
Produce electricity as long as they are supplied with fuel (hydrogen) inline batteries that will eventually run out
Only by product is water
Clean alternative (environmentally friendly)
More expensive
Hydrogen flammable so careful handling and storage
Advantages + disadvantages of rechargeable cells (batteries)
-ideal for portable devices
-Less expsive than hydrogen fuel cell
-Easy to use
-limited range need to be reachrged
-environmental impacts when disposing of
At the anode hydrogen fuel cells half equation - remember anode is the negative electrode in hydrogen fuel cells
Oxidation of hydrogen :
2H2 —> 4H+ + 4e
How hydrogen fuel cells work
- Hydrogen comes in from the leftoutlet and is oxidised by the anode
- Hydrogen atom loses an e,et rom to be come H+ ions
- Hydrogen ions move over the electrolyte to the cathode
- They then react to make water (reduced)
At the cathode hydrogen fuel cells half equations- remember the cathode is positive as it is the other way around
O2 + 4H+ +4e- —> 2H2O
Overall hydrogen fuel cell equation
2H2 + O2 —> 2H2O