energy changes CGP Flashcards
why does the overall amount of energy in the universe stay same after a chemical reaction
energy is conserved in chemical reactions, moved around ( not created/ destroyed)
-examples of exothermic reactions- the temperature of surroundings increase x3
-describe what each is or give an example
-everyday uses of exothermic reactions x2
-combustion
neutralisation
oxidation
(also physical processes like freezing)
-combustion- burning fuels
neutralisation- an acid + alkali
oxidation- eg sodium added to water releases energy ( sodium moves on surface of water as it is oxidised)
-hand warmers- (exothermic oxidation of iron in air releases energy)
self heating cans- (exothermic reaction of chemicals in the base of can)
examples of endothermic reactions x2
everyday uses of endothermic reactions x1 and very brief description of how it works
-thermal decomposition
-reaction of citric acid and sodium hydrogencarbonate
( also physical processes like melting)
- sports injury pack- chemical reaction makes pack cooler instantly
which is endothermic/ exothermic- breaking bonds/ forming bonds
what is activation energy
energy supplied to break bonds- endothermic
energy released when bonds formed- exothermic
minimum amount of energy particles need to collide with eachother and react
what are the axis in reaction profiles
what are the labels you could be asked to add
equation to work out overall energy change using bond energies
energy- y axis
progress of reaction- x axis
activation energy
for exo- energy release
for endo- energy absorbed
energy required to break bonds - energy released by forming bonds
compare energy from bonds in an exothermic and endo reaction
exo- energy released from forming bonds greater than energy needed to break bonds
endo- energy needed to break bonds greater than energy released from forming new bonds
5 parts of simple chemical cell- explain them
describe 5 steps to a simple chemical cell
-2 different electrodes- materials that conduct electricity- usually metal
electolyte- liquid containing ions
wire
voltemeter- measures voltage of cell
beaker
-2 different electrodes in contact with an electrolyte.
-the (metal) ions in electrodes react with the ions in the electrolyte
- chemical reactions between electrodes and electrolyte set up a charge difference between electrodes.
-wire connects electrodes so charge can flow and electricity produced
-can connect voltemeter to measure voltage
describe a battery
why does a charge difference/ voltage occur in cells
how can you increase the voltage in a cell
what two things affect the size of voltage in a cell
what are the reactant particles in a cell
2 or more cells connected in series to provide greater voltage
different metals react differently with the same electrolyte
increase the difference in reactivity of the electrodes
1-type of electrodes and reactivity of the electrodes,
2-the electrolyte used
ions in electrolyte + metal ions on electrode
why does changing the electrolyte in a cell affect the size of voltage
because different ions in the electrolyte will react differently with the metal elecrodes
-what makes a non rechargable battery non rechargable
-give 1 example or a battery like this
- why can rechargable batteries be recharged
chemical reactions that happen are irreversible. reactions stop once a reactant is used up
- alkaline batteries
-the reactions are reversed when external electrical current is provided
benefits of hydrogen fuel cells than rechargeable cells/batteries in cars x4 and other fuels x2
what are the 2 by products of hydrogen fuel cells
cons of hydrogen fuel cells x2
dispose of, recharging, cost, energy stored
-batteries( in electric cars) more polluting to dispose- made from toxic metal compounds
-amount of times battery recharged is limited
-batteries more costly to make than fuel cells
- batteries store less energy than fuel cells- need to be recharged more-takes time
- cars with fuel cells produce less pollutants than other fuels
-other fuels are finite - water + heat
-producing hydrogen take alot of energy (usually burning fossil fuels)
-dangerous to store hydrogen as a gas, hard to liquify
in fuel cell, what electrode:
is +ve, -ve. reduction happens, oxidation happens
anode= -ve oxidation cathode= +ve reduction
describe what happens in fuel cell x4
hydrogen at anode and Oxygen at cathode.
Hydrogen is oxidised- splits into H+ ions and e-
e- pass through wire to cathode, forming current.
H+ ions in electrolyte go to cathode
At cathode, O2 gains e- +reacts w/ with H+ ions to form water (reduction)
-what type of reaction takes place in a fuel cell
half equations in fuel cell-
anode, cathode, overall
- redox reaction
anode- 2H¬2 —-> 4H+ + 4e-
cathode- O2 + 4H+ + 4e- —-> 2H¬2O (2 waters)
overall- 2H¬2 + O2 —-> 2H¬2O
(hydrogen + oxygen = water)
what normally used as electrolyte
what else can you use- what ions would be produced at cathode
what material used for electrodes
acid eg phosphoric acid
alkali eg potassium hydroxide OH- ions at cathode
porous carbon with catalyst
