5.5 CHAPTER 5. THE CHEMICAL INDUSTRY
5.5 Electrochemistry and batteries
ESCCQ
You will remember fromchapter 4 that a galvanic cell (also known as a voltaic cell)
is a type of electrochemical cell where a chemical reaction produces electrical energy.
The electromotive force (emf) of a galvanic cell is the difference in voltage between the
two half cells that makeit up. Galvanic cells have a number of applications, but one of
the most important is their use in batteries. You will know from your own experience
that we use batteries ina number of ways, including cars, torches, sound systems and
cellphones to name justa few.How batteries work ESCCR
A battery is a device inwhich chemical energy is directly converted to electrical en-
ergy. It consists of one or more voltaic cells, each of which is made up oftwo half
cells that are connectedin series by a conductiveelectrolyte. The voltaic cells are con-
nected in series in a battery. Each cell has a positive electrode (cathode),and a negative
electrode (anode). These do not touch each other but are immersed in asolid or liquid
electrolyte.Each half cell has a net electromotive force (emf)or voltage. The voltage of the battery is
the difference betweenthe voltages of the half-cells. This potential difference between
the two half cells is what causes an electric current to flow.Batteries are usually divided into two broad classes:- Primary batteries irreversibly transform chemical energy to electrical energy. Once
the supply of reactants has been used up, the battery can’t be used any more. - Secondary batteries can be recharged, in other words, their chemical reactions
can be reversed if electrical energy is supplied to the cell. Through thisprocess,
the cell returns to its original state. Secondary batteries can’t be rechargedforever
because there is a gradual loss of the active materials and electrolyte.Internal
corrosion can also takeplace.
Battery capacity and energy ESCCS
The capacity of a battery, in other words its ability to produce an electric charge, de-
pends on a number of factors. These include: