It spans several pages, but it is mostly revision and has been included as a reference for learners. You will need to decide, based on your class, about how much time you need to dedicate revising these topics, or whether you get your learners to read over the content and complete the activity at the end. Can you remember learning about compounds in Gr. We will start this chapter by summarising and revising some of the main ideas about elements and compounds from Gr.
Electrochemical cell An electrochemical cell is a device that produces an electric current from energy released by a spontaneous redox reaction, this can be caused from electricity.
This kind of cell includes the Galvanic cell or Voltaic cell, named after Luigi Galvani and Alessandro Voltaboth scientists who conducted several experiments on chemical reactions and electric current during the late 18th century.
Electrochemical cells have two conductive electrodes the anode and the cathode.
The anode is defined as the electrode where oxidation occurs and the cathode is the electrode where the reduction takes place. Electrodes can be made from any sufficiently conductive materials, such as metals, semiconductors, graphite, and even conductive and electric polymers.
In between these electrodes is the electrolytewhich contains ions that can freely move. The galvanic cell uses two different metal electrodes, each in an electrolyte where the positively charged ions are the oxidized form of the electrode metal.
One electrode will undergo oxidation the anode and the other will undergo reduction the cathode. The metal of the anode will oxidize, going from an oxidation state of 0 in the solid form to a positive oxidation state and become an ion.
This forms a solid metal that electrodeposits on the cathode. The two electrodes must be electrically connected to each other, allowing for a flow of electrons that leave the metal of the anode and flow through this connection to the ions at the surface of the cathode.
This flow of electrons is an electric current that can be used to do work, such as turn a motor or power a light. A galvanic cell whose electrodes are zinc and copper submerged in zinc sulfate and copper sulfaterespectively, is known as a Daniell cell.
A shot glass -shaped container is aerated with a noble gas and sealed with the Teflon block. In this example, the anode is the zinc metal which is oxidized loses electrons to form zinc ions in solution, and copper ions accept electrons from the copper metal electrode and the ions deposit at the copper cathode as an electrodeposit.
This cell forms a simple battery as it will spontaneously generate a flow of electric current from the anode to the cathode through the external connection. This reaction can be driven in reverse by applying a voltage, resulting in the deposition of zinc metal at the anode and formation of copper ions at the cathode.
The simplest ionic conduction path is to provide a liquid junction. To avoid mixing between the two electrolytes, the liquid junction can be provided through a porous plug that allows ion flow while reducing electrolyte mixing.
To further minimize mixing of the electrolytes, a salt bridge can be used which consists of an electrolyte saturated gel in an inverted U-tube.
As the negatively charged electrons flow in one direction around this circuit, the positively charged metal ions flow in the opposite direction in the electrolyte. A voltmeter is capable of measuring the change of electrical potential between the anode and the cathode. Electrochemical cell voltage is also referred to as electromotive force or emf.
A cell diagram can be used to trace the path of the electrons in the electrochemical cell. For example, here is a cell diagram of a Daniell cell: This is separated from its oxidized form by a vertical line, which represents the limit between the phases oxidation changes.
The double vertical lines represent the saline bridge on the cell. Finally, the oxidized form of the metal to be reduced at the cathode, is written, separated from its reduced form by the vertical line. The electrolyte concentration is given as it is an important variable in determining the cell potential.
Standard electrode potential[ edit ] To allow prediction of the cell potential, tabulations of standard electrode potential are available. Such tabulations are referenced to the standard hydrogen electrode SHE. The SHE electrode can be connected to any other electrode by a salt bridge to form a cell.
If the second electrode is also at standard conditions, then the measured cell potential is called the standard electrode potential for the electrode. The standard electrode potential for the SHE is zero, by definition.
The polarity of the standard electrode potential provides information about the relative reduction potential of the electrode compared to the SHE. If the electrode has a positive potential with respect to the SHE, then that means it is a strongly reducing electrode which forces the SHE to be the anode an example is Cu in aqueous CuSO4 with a standard electrode potential of 0.
The oxidation potential for a particular electrode is just the negative of the reduction potential.
A standard cell potential can be determined by looking up the standard electrode potentials for both electrodes sometimes called half cell potentials.
The one that is smaller will be the anode and will undergo oxidation. The cell potential is then calculated as the sum of the reduction potential for the cathode and the oxidation potential for the anode.
By definition, the electrode potential for the SHE is zero. Spontaneity of redox reaction[ edit ] Main article: The emf of the cell at zero current is the maximum possible emf.This page contains Questions on New () GCSE AQA Chemistry C4 Chemical Calculations along with textbook kerboodle answers, videos and past paper questions for revision and understanding of the topic C4 Chemical Calculations.
This is the complete revision pack for New () GCSE AQA Chemistry C4 Chemical Calculations. Chemistry notes on the physical properties of lithium, sodium, potassium, rubidium, caesium (cesium) and francium, The chemical properties, chemical reactions with water, oxygen and chlorine - word equations & balanced equations and uses of the elements and compounds of the Group 1 Alkali Metals of the Periodic Table e.g.
lithium, sodium & potassium etc. Write a balanced chemical equation for the following decomposition reaction: aluminum is obtained from aluminum oxide with the addition of a large amount of electrical energy 2Al2O3 -energy-> 4Al + 3O2. Write the balanced equation for this reaction. and hydrogen gas.
tantalum metal reacts with chlorine gas to form tantalum pentachloride. This reaction is an important industrial source of phosphoric acid.
Dec 04, · Write the balanced equation for this decomposition reaction. Iron(II) chloride, FeCl2, reacts with water at high temperatures to form triiron tetraoxide (Fe3O4), hydrochloric acid, and hydrogen pfmlures.com: Resolved.
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