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 Year 12 Chemistry

HSC Assessment Task 1-12

Production of Materials

Primary and Secondary Cells

Dry cell in comparison with Fuel cell

Fuel cell is galvanic cell based device, basically using a chemical

reaction of different kinds of fuel ( including Hydrogen, methanol,

ethanol, natural gas and gasoline) with a oxidizing agent to produce

electric current (electricity), it is first invented by a British Physicist,

William Grove in 1839. The most common fuel cell uses hydrogen as

its fuel to undergo redox reaction with air (oxygen) from the

atmosphere to produce electricity and heat.

Describes the chosen cells as being Galvanic cells

- Dry Cell (primary cell)

 

Dry cells are so-called because its electrolytes are in a solid orpastes from base on a galvanic cells but rather that using liquids

(solution), it is more suitable and less dangerous in many

applications. The most common dry cell is the zinc and graphite

battery with a voltage between 1.2 -1.5 volts. A redox reaction

happens with in the dry cell where zinc gives of electrons, under

going oxidation and on the other side, a graphite pin surrounding by a

paste containing manganese dioxide, gains the electrons and under

going reduction.

 

- Fuel Cell

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A galvanic cell is a device which convert chemical energy to

electrical energy. Fuel cells is such a devics which can continuously

converting chemical energy to electrical energy and produce between

0.6 - 0.8 volts of electricity by using hydrogen as a fuel. Hydrogen

fuel cell are made up of three different segments which are

sandwiched together: the anode, the electrolyte and the cathode.

Electrons are given up by the hydrogen anode (negative) and flows

from the anode via the circuit to the cathode (positive) where they

are gained by cations. The hydrogen becomes ions which then pass

through the electrolyte (membrane) to the cathode (oxygen),

combining together to produce water.

Explains how the chosen cells are Galvanic cells in terms of oxidation

and reduction

- Fuel cell

 The redox reaction happens between the anode (hydrogen) and

(oxygen). At the anode a catalyst oxidizes the fuel (hydrogen) where

the hydrogen are splited into positively charged ions and negatively

charged electrons. The electrons flows through an external circuit to

the cathode and are gained by the oxygen in order to complete the

other half of the reaction. The use of electrolyte usually defines the

type of fuel cell, a proton exchange membrane fuel cells (hydrogen

fuel cell) use a solid polymer membrane (a thin plastic film) as the

electrolyte. The electrolyte is designed so ions can pass through

where as the electrons can't.

2H2 --------> 4H+ + 4e- OxidationAnode

(-)

O2 + 4H+ + 4e- -------> 2 H2OReduction

Cathode(+)

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-Dry Cell

The ordinary dry cell is a primary cell incorporating the oxidation of 

zinc and the reduction of manganese dioxide. The dry cell can

produce approximately 1.5 volts of emf (electromotive force). The

manganese dioxide paste also contains ammonium chloride and zinc

chloride which are the mainly used electrolyte in a dry cell. The dry

cell contains a zinc anode(-), mainly in the form of a cylindrical, everyzinc atom loses 2 electrons and gains by manganese dioxide through

the graphite(carbon) cathode(+). The graphite cathode are

surrounded by and mixed with manganese dioxide in order to

increase the electrical conductivity , the graphite pin are usually

placed in the central of the cell.

Overall reaction: Zn(s) +2MnO2(s) +2NH4Cl(aq) Mn→ 2O3(s)

+Zn(NH3)2Cl2 (aq) +H2O(l)

Zn(s) Zn→2+(aq) + 2e− 

Oxidation

Anode

(-)

2MnO2(s) + 2e− + 2NH4Cl(aq) Mn→ 2O3(s) +

2NH3(aq) + H2O(aq) + 2 Cl− 

Reduction

Cathode

(+)

the Cl− combines with the Zn2+ and manganese is

reduced from an oxidation state of (+4) to (+3).

operation of a dry cell providing electrical energy

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Discusses the cost and practicality of each cell

Fuel cell has a high practicality in comparison to other energy

sources. Fuel cell are widely used in different area within the society

such as for commercial and industrial (usually as a back up power),because of using hydrogen as fuel, this makes the fuel cell system

surprisingly light in weight and small in size. One of the biggest

advantage of fuel cell is that the system can work continually for a

very long period of time as long as the fuel supply are stable, this is

because fuel cells have no moving parts and does not involve

combustion, therefore, fuel cell are highly suitable and useful power

supply particularly in remote locations such as aircraft, vehicles,

submarine and even spacecraft. Fuel cell can also convert its heat

energy in by using catalyst and without cooling down the steam, the

energy of fuel cell can go up to 70% conversion efficiency. Fuel cell

can also changes its voltage where as the dry cell cannot.

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Cost - in 2003, the cos of electricity generated by a fuel cell was

around US $100 - $200 per kilowatt, in 2009 was US $61 per kilowatt

and by the time of 2015, the cost will be less than 30 dollars per

kilowatt, this is due to the reduction of the price of the catalyst and

membrane (the electrolyte). This is immensely cheap and affordable

for costumers for such a long life energy sources.

Dry cell or battery are relatively cheap compared to other types of 

portable power sources. Dry cell comes in a range of sizes to suit

most applications, from small AAA cells through to large 9V batteries.

Battery has been a every day living energy sources throughout the

world as it is inexpensive to produce, dry cell are easy to store and

use, although it can leak, but it's very useful when a small current is

needed, it is also the main power sources of low drain appliances

such as torches, clocks, radios. Although dry cell battery are non-

rechargeable and have a short shelf life as it can deteriorate, leak

and can go "dead" rapidly, but such a low cost makes it cheap to

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replace.

Discusses the cells' impact on society

Dry cell battery are the first commercial battery developed in 1866and had a massive impact on society which is still being fully realised.

As the first type of reliable electricity, dry cell led to society becoming

extremely more mobile and convenient, many electrical appliances

had no longer need to be plugged in to a power outlet, allowing us

more easily to have connect with such everyday items used in

education, entertainment and everyday living. This has a significant

impact society as dry cell have improved people’s quality of life.

Furthermore, especially in more modern times, dry cells have paved

the way for the miniaturisation of electrical devices through their own

compost size. Dry cells had also paved the way for the future

development of batteries.

Fuel cell also have a huge impact on society as it is seeing as the

future power sources with a huge potential. Fuel cell have hight

efficiency and relatively smell mass. Other advantage of fuel cell in

terms of environmental impact and the productivity has led the fuel

cell technology becoming one of the more suitable energy sources in

the future. Many new fuel cell systems have been developed such as

the Combined heat and power (CHP) fuel cell systems in order toimprove the fuel cell technology.

Discusses the cells' environmental impact

Fuel cells have a lot less impact on the environment in comparing

with dry cell as it is a renewable device, in the hydrogen fuel cell,

water and heat are the only product in the reaction, all materials used

in the fuel cells cause no environmental damage and can be

produced without any problems, it is non-polluting as water is

harmless to the environment and most importantly to the human

body. About 50% of the world's carbon pollution comes from vehicles,

using a fuel cell vehicle and other fuel cell based devices help

reducing carbon pollution.

The environment impact of dry cell have always been an issue

concerned as the dry cell is a non rechargeable and non renewable

power sources, dry cell must be abandoned ones they are used up

and the reaction is no longer reacting which will end up in our landfills

and have effect on the land. These waste must be treated cautiouslyas the dry cell is made from zinc, a heavily toxic metal which courses

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harmful to human and other animal species.

Bibliography:

Batterytype

Structure Chemistry Cost andpracticality

Impact on societyand environment

Dry cell Outer zinc casing(anode) with agraphite rod(cathode) in a pasteof manganese dioxideand ammoniumchloride as theelectrolyte.

Oxidation at theanode:Zn(s) Zn→

2+(aq) + 2e−

Reduction at thecathode: 

2MnO2(s) + 2 e− +2NH4Cl(aq) → Mn2O3(s) + 2NH3(aq)+ H2O(aq) + 2 Cl−

- cell cannot berecharged- short shelf life as itcan deteriorate andleak- can go "dead"rapidly- inexpensive toproduce- small, lightweightweight

- mobile and convenientto use for applianceswith infrequent use; e.g. Torch, calculators- considerations for safedisposal after discharged- harmful to human andother animal species.

Fuel cell  Two half cell areseparated by amembrane; hydrogenand oxygen arepumped into the cellwhere the chemicalenergy of hydrogen isconverted intoelectrical energythrough a redoxreaction.

Oxidation at theanode:2H2 → 4H+ + 4e-

Reduction at thecathode:O2 + 4H+ + 4e- 2→  H2O

- greater efficiency- less maintenance- longer life span- can operate athighertemperatures.- higher cost

- well suited powersources for vehicles andwill produce lesspollution.- reduce carbon pollution

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http://www.fuelcells.org/info/library/QuestionsandAnswers062404.pdf 

http://www.fuelcellmarkets.com/fuel_cell_markets/proton_exchange_m

embrane_fuel_cells_pemfc/4,1,1,2502.html ,Fuel Cell Markets Ltd.

http://en.wikipedia.org/wiki/Dry_cell#Dry_cell 3 November 2011, the

free encyclopedia

Chemistry Contexts Second edition (HSC), Debbie Irwin, Ross Farrelly,

Deborah Vitlin, Patrick Garnett, 2006

http://en.wikipedia.org/wiki/Fuel_cell 31 October 2011, wikipedia, the

free encyclopedia

http://en.wikipedia.org/wiki/Proton_exchange_membrane_fuel_cell 19

September 2011

http://www.ehow.com/about_6398485_lithium-ion-vs_-alkaline-

batteries.html 

P.1 image from:

http://upload.wikimedia.org/wikipedia/en/thumb/1/1b/Fuel_Cell_Block_Diagram.svg/400px-

Fuel_Cell_Block_Diagram.svg.png 

P.2 image

from:http://www.fuelcellmarkets.com/content/images/articles/1/Fc_diagram_pem.gif  

http://www.fuelcellmarkets.com/fuel_cell_markets/proton_exchange_membrane_fuel_cells_pemfc/

4,1,1,2502.html 

P.3 image from: http://www.odec.ca/projects/2006/glaz6j2/battery_encarta.JPG 

P.4 image from: http://www.fuelcells.org/info/library/QuestionsandAnswers062404.pdf   p.3

http://upload.wikimedia.org/wikipedia/commons/6/68/Hydrogen_vehicle.jpg