Presentation is loading. Please wait.

Presentation is loading. Please wait.

Boardworks A2 Chemistry Applications of Redox Chemistry

Similar presentations


Presentation on theme: "Boardworks A2 Chemistry Applications of Redox Chemistry"— Presentation transcript:

1 Boardworks A2 Chemistry Applications of Redox Chemistry

2 Boardworks A2 Chemistry Applications of Redox Chemistry
Teacher notes In ‘Slide Show’ mode, click the name of a section to jump straight to that slide.

3 Electrochemical cells
Boardworks A2 Chemistry Applications of Redox Chemistry Redox reactions involve the transfer of electrons between two species. The flow of electrons is an electrical current. Redox reactions can therefore be used to generate electrical current. This is the basis of batteries and fuel cells. An electrochemical cell is a store of chemical energy in a closed system. Photo credit © 2010 shutterstock.com / Tatiana Popova Teacher notes See the ‘Redox Chemistry and Electrode Potentials’ presentation for more information about redox reactions. All reactants and products are contained within the casing of the cell.

4 Rechargeable and non-rechargeable cells
Boardworks A2 Chemistry Applications of Redox Chemistry There are two types of cell: non-rechargeable and rechargeable. They are also known as primary and secondary cells. Primary cells can only be used once. Secondary cells can be recharged and reused. Photo credit (left) © 2010 shutterstock.com / Adam Majchrzak Photo credit (right) © 2010 shutterstock.com / Tatiana Popova Smaller cells contain fewer reactants and produce less electrical energy. However, the reaction voltage doesn’t change with cell size.

5 Boardworks A2 Chemistry Applications of Redox Chemistry
How does a cell work? Boardworks A2 Chemistry Applications of Redox Chemistry

6 Boardworks A2 Chemistry Applications of Redox Chemistry
Primary cells Boardworks A2 Chemistry Applications of Redox Chemistry A primary cell can only be used once because it transfers stored chemical energy into electrical energy by a non-reversible chemical reaction. Primary cells are usually cheaper to buy. They are more reliable as they do not discharge much when they are not in use. This makes them more useful for applications such as smoke detectors. Teacher notes You could encourage students to think of other applications where primary cells are more useful, e.g. in an emergency torch. Carbon–zinc dry cell Alkaline dry cell

7 Boardworks A2 Chemistry Applications of Redox Chemistry
Secondary cells Boardworks A2 Chemistry Applications of Redox Chemistry Teacher notes You could ask students to debate what makes a good cell, e.g. large energy to mass ratio, affordable, can be recharged many times, does not dissipate much energy on standing, is safe, easy to recycle, etc. Students will not be required to recall specific types of cells.

8 Reactions in a zinc–carbon cell
Boardworks A2 Chemistry Applications of Redox Chemistry

9 Primary or secondary cells?
Boardworks A2 Chemistry Applications of Redox Chemistry

10 Boardworks A2 Chemistry Applications of Redox Chemistry
Batteries Boardworks A2 Chemistry Applications of Redox Chemistry A battery is more than one cell connected together in a series arrangement. When a conductor is connected across the two terminals, a circuit is formed and electrons flow through it. By connecting more than one cell together, the electromotive force is increased. The battery voltage is the sum of the voltages of each of the cells. Teacher notes You may wish to point out that cells are often called batteries in everyday life, despite this being technically incorrect. However, when more than one cell is put together in series inside an appliance they then become part of a battery. A battery is a closed system which contains the high energy reactants and the low energy products in a sealed unit.

11 Boardworks A2 Chemistry Applications of Redox Chemistry
Lead-acid battery Boardworks A2 Chemistry Applications of Redox Chemistry

12 Boardworks A2 Chemistry Applications of Redox Chemistry
Calculate the e.m.f Boardworks A2 Chemistry Applications of Redox Chemistry

13 Boardworks A2 Chemistry Applications of Redox Chemistry
Teacher notes In ‘Slide Show’ mode, click the name of a section to jump straight to that slide.

14 Boardworks A2 Chemistry Applications of Redox Chemistry
Fuel cells Boardworks A2 Chemistry Applications of Redox Chemistry A fuel cell converts chemical energy into electrical energy in a similar fashion to a battery. However, a fuel cell is an open system – reactants flow in and products flow out, rather than being stored in the cell. Fuel cells are used in spacecraft and in hydrogen powered cars. Photo credit: Ford Motor Company / NREL Looking under the hood of a fuel cell car that was developed by Ford Motor Company Teacher notes You may wish to extend students by explaining that there is a third type of system – isolated. This is achieved when neither matter nor energy can flow into or out of the system.

15 Boardworks A2 Chemistry Applications of Redox Chemistry
Hydrogen fuel cells Boardworks A2 Chemistry Applications of Redox Chemistry Hydrogen fuel cells have been used in spacecraft for many years. New developments are incorporating them into cars to replace the internal combustion engine. In a hydrogen fuel cell, hydrogen and oxygen gases react to form water. At the anode: 2H2(g) 4H+(aq) + 4e– At the cathode: Teacher notes You may have a sample hydrogen fuel cell at school which can be used for demonstration. See the ‘Redox Chemistry and Electrode Potentials’ presentation for more information about combining half equations. 4H+(aq) + O2(g) + 4e– 2H2O(l) Overall equation: 2H2(g) + O2(g) 2H2O(l)

16 How does a hydrogen fuel cell work?
Boardworks A2 Chemistry Applications of Redox Chemistry Teacher notes The white arrows represent hydrogen gas and the red arrows represent oxygen gas.

17 Boardworks A2 Chemistry Applications of Redox Chemistry
Label the fuel cell Boardworks A2 Chemistry Applications of Redox Chemistry

18 Production of hydrogen
Boardworks A2 Chemistry Applications of Redox Chemistry Hydrogen is a very reactive element and must be produced by a chemical reaction before it can be used in a fuel cell. There are currently two main methods of manufacturing hydrogen: reaction of hydrocarbons with steam electrolysis of acidified water. Although a hydrogen fuel cell is not directly polluting, processes used to produce hydrogen can be. Electricity for electrolysis is often produced by fossil fuel power stations. Carbon dioxide is produced from the reaction of hydrocarbons with steam. Teacher notes You may wish to demonstrate the production of hydrogen from the electrolysis of water, using a Hoffman Voltameter. You could explain to students that although hydrogen releases energy on oxidation, often more energy is used for electrolysis and transport of the hydrogen than is released. Hydrogen can also be produced from cracking alkanes.

19 Transporting and storing hydrogen
Boardworks A2 Chemistry Applications of Redox Chemistry Teacher notes You could ask students to generate a list of disadvantages of using hydrogen as a fuel, e.g. limited filling stations, cost of hydrogen, containers have to be robust so that in a crash they do not explode.

20 Boardworks A2 Chemistry Applications of Redox Chemistry
Hydrogen-rich fuels Boardworks A2 Chemistry Applications of Redox Chemistry With the difficulty in transporting and storing hydrogen, some fuel cell vehicles use hydrogen-rich fuels which are converted to hydrogen by an onboard ‘reformer’. The reformer uses temperatures of 250–300°C to favour reactions generating hydrogen gas. Photo credit: Leslie Eudy / NREL This fuel cell bus in Georgetown University R&D program uses an onboard methanol reformer to provide hydrogen power to the fuel cell. Hydrogen-rich fuels include methanol, natural gas and petrol.

21 Direct methanol fuel cells
Boardworks A2 Chemistry Applications of Redox Chemistry Teacher notes The white arrows represent methanol and the red arrows represent oxygen gas. Methanol is manufactured in advance by one of two methods: steam methane reforming or reacting carbon monoxide with hydrogen. Water must be purified before it can be used in this fuel cell. You may wish to ask students to debate the benefits and drawbacks of using a methanol fuel cell.

22 Reactions in a direct methanol fuel cell
Boardworks A2 Chemistry Applications of Redox Chemistry

23 Boardworks A2 Chemistry Applications of Redox Chemistry
Ethanol fuel cell Boardworks A2 Chemistry Applications of Redox Chemistry Ethanol is a less toxic and more energy-dense alcohol than methanol. Research into developing an ethanol fuel cell is ongoing. Currently, platinum-based catalysts are used to oxidize ethanol, but don’t achieve complete oxidation. Cheaper, more efficient catalysts capable of fully oxidizing ethanol are needed. Photo credit: Warren Gretz / NREL Ethanol fuel pump. Teacher notes See the Boardworks AS Chemistry ‘Green Chemistry’ presentation for more information about carbon neutral fuels. Ethanol can be made from renewable sources, such as the fermentation of sugar. These energy resources are considered carbon neutral – the amount of carbon dioxide they release is equal to the amount absorbed during growth.

24 Fuel cell vs. conventional vehicles
Boardworks A2 Chemistry Applications of Redox Chemistry

25 Boardworks A2 Chemistry Applications of Redox Chemistry
Hydrogen economy Boardworks A2 Chemistry Applications of Redox Chemistry

26 Modern breath alcohol testers
Boardworks A2 Chemistry Applications of Redox Chemistry Fuel cell technology has been applied to breath alcohol testers. Ethanol in a person’s breath is oxidized into carbon dioxide and water, producing a measurable electrical current. electrical current ethanol from breath oxygen Teacher notes You may wish to ask students on the Edexcel course to research the other types of breath alcohol testers available, based on the use of IR or the reduction of chromium compounds. They could compare these models to the fuel cell model. water acid–electrolyte membrane platinum cathode platinum anode

27 Boardworks A2 Chemistry Applications of Redox Chemistry
Teacher notes In ‘Slide Show’ mode, click the name of a section to jump straight to that slide.

28 Boardworks A2 Chemistry Applications of Redox Chemistry
Glossary Boardworks A2 Chemistry Applications of Redox Chemistry Teacher notes adsorption – The process by which a substance is held on the surface of another material. alkaline dry cell – A type of primary cell consisting of zinc and manganese oxide electrodes with an electrolyte paste. anode – The positive electrode, where oxidation takes place. battery – More than one cell connected in series. carbon neutral – Any activity that produces no overall emissions of carbon dioxide. cathode – The negative electrode, where reduction takes place. closed system – A system where matter cannot flow in or out, but energy can. direct methanol fuel cell – A device that converts methanol into energy, water vapour and carbon dioxide, without first converting methanol into hydrogen. electrochemical cell – Two half cells connected by a salt bridge, creating a potential difference that can be used to produce a current. electrolyte – A substance than can conduct electricity. electromotive force (e.m.f.) – The voltage produced by a cell when no current flows. fuel cell – A device that uses the reaction of a fuel with oxygen to produce electrical energy, in an open system. hydrogen economy – A proposed system in which hydrogen is the primary energy carrier. negative terminal – An electrical contact from which electrons flow. open system – A system that energy and matter can flow into and out of. porous separator – Acts as the salt bridge in a cell. positive terminal – An electrical contact that electrons flow towards through an external circuit. primary cell – An electrochemical cell that converts stored chemical energy into electrical energy in a non-reversible chemical reaction. proton exchange membrane (PEM) – A polymer material which only allows protons to pass through it. redox reaction – A chemical reaction that involves an oxidation and a reduction. secondary cell – An electrochemical cell that converts stored chemical energy into electrical energy in a reversible chemical reaction. terminal – An electrical contact connecting a cell or battery to an external circuit.

29 Boardworks A2 Chemistry Applications of Redox Chemistry
What’s the keyword? Boardworks A2 Chemistry Applications of Redox Chemistry

30 Boardworks A2 Chemistry Applications of Redox Chemistry
Multiple-choice quiz Boardworks A2 Chemistry Applications of Redox Chemistry


Download ppt "Boardworks A2 Chemistry Applications of Redox Chemistry"

Similar presentations


Ads by Google