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Unit 5: Energy Changes - Coggle Diagram
Unit 5: Energy Changes
Exothermic
Energy released to the surroundings
Examples
Combustion
Respiration
Temperature
increase
Overall enthalpy change
> 0
Negative number
Endothermic
Energy taken in from surroundings
Examples
Changing of state such as melting
Temperature
decrease
Overall enthalpy change
< 0
Positive Number
Chemical cells and Fuel cells
Electrochemical cell is a basic system of
two different electrodes
in contact with an electrolyte
Electrolyte is a
liquid that contains ions
which react with the electrodes
Voltage
factors
Type of electrodes
used
Different metals react differently
with the
same electrolyte
The
least reactive metal
is the
positive electrode
The bigger the
difference in reactivity series,
the
bigger the voltage
of the cells
Electrolyte
used
Different ions in solution will react differently to electrodes
Batteries
Two or more cells
connected in series
Have
toxic metal compunds
and their
disposal causes pollution
Will
evantually run out
Must be
replaced after a number of recharges
Calculating Voltage
Most reactive - least reactive = p.d
Fuel cells
Produce electricity
using a reaction between an external fuel soruce
(hydrogen) and oxygen
Advantages and Disadvantages
Less polution
than traditional methods
High efficiency
Reliable
Compact and lightweight
Can be used
indefinitely
Produce more energy
per gram of Hydrogen relative to petrol
Hydrogen has to be
stored at high pressures
and it is
explosive
The oxidation of hydrogen generates a voltage
ANODE:
Hydrogen pumped in to make ions
as
oxidation
happens at the
anode
Hydrogen
molecules -->
Hydrogen ions + electrons
CATHODE
:
Oxygen is pumped
.
Water is formed
as
O2 reacts with the H+ ions that moved through
the electrolyte to the anode
Hydrogen
ions +
oxygen
molecules -->
Water
:
Reaction Profiles
Activation energy
Amount of energy needed to start the reaction
Catalysts reduce activation energy
Provide an alternative chemical path
Raj's Matchmaker analogy
Therefore, increaes reaction rate
BB-BM
If BB > BM, ENDO
If BB < BM, EXO
