topic 5 - energy changes

Question 1

energy transfer in exothermic reaction

Answer 1

transfers energy into the surroundings showing a rise in temp

Question 2

examples of an exothermic reaction

Answer 2

• combustion
• neutralisation
• hand warmers

Question 3

energy transfer in endothermic reaction

Answer 3

takes in energy from the surroundings showing a fall in temp

Question 4

examples of an endothermic reaction

Answer 4

• thermal decomposition
• cool parks - sports injuries

Question 5

energy transfer practical

Answer 5

• 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

Question 6

exothermic reaction profile diagram

Answer 6

products lower than reactants

Question 7

endothermic reaction profile diagram

Answer 7

products higher than reactants

Question 8

whats a electrochemical cell

Answer 8

uses chemical reactions to produce electricity

Question 9

how can you make a cell

Answer 9

• connect 2 different electrodes with a wire in the electrolyte
• sometimes a voltmeter to measure the voltage

Question 10

what are batteries

Answer 10

• 2 or more cells connected together in series to provide and greater voltage

Question 11

factors that effect the voltage of a cell

Answer 11

• metal used - greater reactivity the higher the voltage
• type and concentration of electrolyte
• conditions - eg temp

Question 12

rechargeable cells and batteries

Answer 12

can be recharged bc the chem reactions are reversed when external electrical current is supplied - laptops/ phones etc ….

Question 13

non rechargeable cells and batteries

Answer 13

chemical reaction stops when one of the reactants has been used uo - smoke alarms etc….

Question 14

what is a fuel cell

Answer 14

• type of electrochemical cell
• convert chemical energy of fuel and oxygen into electrical enegry to power things

Question 15

hydrogen oxygen fuel cell

Answer 15

combines hydrogen and oxygen to form water which generates lots of electrical enegery

Question 16

fuel cell anode and cathode

Answer 16

ANODE - NEGATIVE - LEFT
CATHODE - POSITIVE - RIGHT

Question 17

anode and cathode compartment - structure of fuel cell

Answer 17

• hydrogen enters anode c
• oxygen enters cathode c
• when reaction over all the water and heat leaves through cathode outlet

Question 18

how does a fuel cell work

Answer 18

1. hydrogen enters from left and oxidised by anode so looses an electron
2. these lost electrons move around the wire to the cathode
3. but the hydrogen ions move across the electrolyte to the cathode
4. they then combine with the oxygen ions that enter form the right and then combine to make water

Question 19

summary of fuel cells

Answer 19

• fuel enters the cell
• gets oxidised
• this creates potential difference
• which drives electrons around the circuit
• which generates electricty

Question 20

pros of fuel cells

Answer 20

• only need hydrogen and oxygen
• dont produce co2
• last longer than batteries

Question 21

cons of fuel cells

Answer 21

• 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

Question 22

what happens to bonds during a chemical reaction

Answer 22

• energy SUPPLIED to BREAK them in the REACTANTS
• energy RELEASED to FORM them in the PRODUCTS

Question 23

whats activation energy

Answer 23

the minimum energy required for a reaction to take place between reacting particles