topic 5 - energy changes Flashcards
(23 cards)
energy transfer in exothermic reaction
transfers energy into the surroundings showing a rise in temp
examples of an exothermic reaction
- combustion
- neutralisation
- hand warmers
energy transfer in endothermic reaction
takes in energy from the surroundings showing a fall in temp
examples of an endothermic reaction
- thermal decomposition
- cool parks - sports injuries
energy transfer practical
- take temp of the reagents
- mix them in a polystyrene cup
- measure the temp of the solution afterwards
- put polstyrene cup in beaker of cotton wall to prevent eneegry being lost into the surroundings - insulation
- add a lip to prevent evaporation
exothermic reaction profile diagram
products lower than reactants
endothermic reaction profile diagram
products higher than reactants
whats a electrochemical cell
uses chemical reactions to produce electricity
how can you make a cell
- connect 2 different electrodes with a wire in the electrolyte
- sometimes a voltmeter to measure the voltage
what are batteries
- 2 or more cells connected together in series to provide and greater voltage
factors that effect the voltage of a cell
- metal used - greater reactivity the higher the voltage
- type and concentration of electrolyte
- conditions - eg temp
rechargeable cells and batteries
can be recharged bc the chem reactions are reversed when external electrical current is supplied - laptops/ phones etc ….
non rechargeable cells and batteries
chemical reaction stops when one of the reactants has been used uo - smoke alarms etc….
what is a fuel cell
- type of electrochemical cell
- convert chemical energy of fuel and oxygen into electrical enegry to power things
hydrogen oxygen fuel cell
combines hydrogen and oxygen to form water which generates lots of electrical enegery
fuel cell anode and cathode
ANODE - NEGATIVE - LEFT
CATHODE - POSITIVE - RIGHT
anode and cathode compartment - structure of fuel cell
- hydrogen enters anode c
- oxygen enters cathode c
- when reaction over all the water and heat leaves through cathode outlet
how does a fuel cell work
- hydrogen enters from left and oxidised by anode so looses an electron
- these lost electrons move around the wire to the cathode
- but the hydrogen ions move across the electrolyte to the cathode
- they then combine with the oxygen ions that enter form the right and then combine to make water
summary of fuel cells
- fuel enters the cell
- gets oxidised
- this creates potential difference
- which drives electrons around the circuit
- which generates electricty
pros of fuel cells
- only need hydrogen and oxygen
- dont produce co2
- last longer than batteries
cons of fuel cells
- hydrogen is a gas so takes up loads of space
- explosive when mixed with air
- to make the fuel in the first place you need energy
what happens to bonds during a chemical reaction
- energy SUPPLIED to BREAK them in the REACTANTS
- energy RELEASED to FORM them in the PRODUCTS
whats activation energy
the minimum energy required for a reaction to take place between reacting particles
