Current Electricity Part 2 Potential Difference and Electrochemical Cells

Electrochemical Cells A Battery: is a combination of electrochemical cells Each electrochemical cell is a package of chemicals that converts chemical energy into electrical energy An electrolyte is a liquid or paste that conducts electricity because it contains chemicals that form ions. An example is citric acid. Electrodes are metal strips that react with the electrolyte. Two different electrodes, such as zinc and copper, are used in a battery. One of the electrodes collects electrons. This is the negative electrode. The other electrode loses electrons. This is the positive electrode.

1) True or false: This is an electrochemical cell. 2) Identify the electrolyte 3) Identify the two electrodes 4) Which electrode gains electrons? What is its charge? 5) Which electrode loses electrons? What is its charge?

Electrochemical Cells Essentially all electrochemical cells have the same components: Electrolyte Positive electrode Negative electrode For this reason, you can make a battery from something as simple as a lemon, a nail, and a penny. Don’t expect it to have many volts, however.

Electrochemical cells Wet cells use a liquid electrolyte Example: car battery Dry cells use a paste electrolyte Example: AA batteries, watch batteries In dry cells, the electrodes can be called terminals. Therefore, you have one negative and one positive terminal. Eventually, the chemicals is a dry cell get used up and charges can no longer be separated.

Electrochemical cells Always recycle dry cells as they contain toxic heavy metals such as nickel, cadmium, and lead. 50% of all of the toxic metals in landfills comes from dry cells that were disposed! Some dry cells are rechargeable. When you recharge a rechargeable battery, the chemical reaction is reversed. The reverse flow of electrons restores the reactants. This prevents you from having to dispose dry cells. A fuel cell generates electricity from a chemical reaction with a fuel such as hydrogen. Their technology will improve in the future. These are used in electrical vehicles.

Potential Difference Potential difference can be thought of as how powerful an energy source is. Think back to previous years Science of the topic of potential energy. Potential energy is stored energy that can be released at any point. An apple on a tree has potential energy. If it falls, its potential energy will be converted to motion. Which apple has higher potential energy? The higher apple of course. When it falls, it will fall at a greater force than the lower apple.

Potential Difference What gives electrons the force to move through a circuit? As you know, electrons have a negative charge. Negative charges are attracted to positive charges. Therefore, to get electrons to move, you need positive charges. Energy sources such as batteries have potential energy. They create negative and positive charges. That is, they create potential difference. In an electrochemical cell, the chemicals in the electrolyte causes a difference in charge between the two terminals. One terminal is given mostly negative charges, and the other is given mostly positives charges. This creates potential difference, because there is now potential energy for the electrons to travel from the negative terminal to the positive terminal.

Potential Difference So the more negative and positive charge is given to the terminals, the more potential difference! The greater the potential difference, the more powerful the energy source! Potential difference is measured in volts (V). High voltage means high potential difference. Remember, high voltage is powerful, therefore it is dangerous!

Voltmeter You can measure voltage with voltmeter. For example, you can measure the voltage of a battery. Place one connecting wire to the negative terminal and the other connecting wire to the positive terminal. An AA alkaline battery would have 1.5 V, or higher. If it’s below 1.3 V, it’s probably not powerful enough, and it needs to be replaced. Rechargeable batteries have lower voltage. However, most devices can still accept them.

Potential Difference

Review Questions What is a circuit? Identify and describe the components of a circuit. What is an electrochemical cell? Name the 3 basic components of an electrochemical cell. What is potential difference? How does it affect the flow of electrons? How is potential difference measured? What are the two types of currents? How is current measured?

Homework Practice Questions on Worksheet Text – Page 436 # 4, 5