Extra Credit 34

List some things that are typically considered when selecting a battery for a new application.

Solution: When selecting a new battery, it is important to first select what type of battery would be appropriate for the application (primary, secondary, or tertiary). Also how long lasting, size, and the voltage supplied from the battery are beneficial to know, because a one cell- 1.5V battery would not be a solid fit for a car battery. Toxicity is important to know just in case there is a crack/leak from the battery.

Different types of batteries: Nickel Metal Hydride, Lithium Ion, Nickel Cadmium, Leak acid, etc

Q12.2.1

Describe the effect of each of the following on the rate of the reaction of magnesium metal with a solution of hydrochloric acid: the molarity of the hydrochloric acid, the temperature of the solution, and the size of the pieces of magnesium.

Solution: An increased molarity will have an increased rate of reaction, because there will be more hydrochloric acid molecules that could react with the magnesium metal. There probability of collision between the will increase. The higher the molarity signifies how concentrated the solution is with that group of molecules. Also an increase in temperature will decrease the activation energy for the reaction and make the reaction run faster. Temperature works as an intermediate to quicken the reaction. The size of magnesium that reacts with the hydrochloric acid needs to be small to increase the speed of the reaction, because the larger the size of magnesium will take a lot longer to react completely.

Q12.5.6

How does an increase in temperature affect rate of reaction? Explain this effect in terms of the collision theory of the reaction rate.

Solution: By increasing the temperature of reaction environment, the activation energy will decrease (which works as a catalyst for the reaction) and increase the rate of the reaction. By increasing the temperature of the environment, the different molecules will begin to move, rotate, and vibrate (in the air, aqueous solution, and even solids) faster and more frequently. The collision theory explains the conditions of gas-phase molecules that need to collide with each other in the correct location on each molecule with a specific amount of energy. Therefore with higher temperatures, there will be more frequent collisions of molecules and will give the molecules more energy through collisions.

Raising the temperature increases the probability of the molecules colliding with one another.

Q21.4.1

What are the types of radiation emitted by the nuclei of radioactive elements?

Solution: There are three types of radiation emitted by the nucleus of radioactive elements: Alpha radiation (α), Beta Radiation (β), Gamma Radiation (γ).

Alpha radiation emits a Helium nucleus (⁴He) from the original nucleus, thus the products will be this alpha particle and another element with a mass number of 4 amu less than the original nucleus and an atomic number of 2 protons less than the original atom.

Beta Radiation has two components to it: Electron emission and Positron Emission. Electron emission releases a charged electron from the original nucleus but the mass number will not change. The products are a new elemental nucleus that is one amu more than the original atomic number, a negative beta particle (an electron), and an anti-neutrino. The Positron emission is similar to the electron emission, but its products will be a neutron that is one amu more than the original atomic number, a positive beta particle, and a neutrino.

Lastly, Gamma radiation usually occurs with the presence of alpha or beta emission and is often emitted with them, however it does not change the mass or atomic number of the nuclei. The gamma rays are a form of ionizing radiation that is more penetrating than alpha or beta particles.

Gamma can be stopped by lead.

Q20.2.5

Of the following elements, which would you expect to have the greatest tendency to be oxidized: Zn, Li, or S? Explain your reasoning.

Solution: Li>Zn>S (in order of tendency to be oxidized). Li has the greatest tendency to be oxidized of the three elements, because the standard reduction potential table determines oxidation and reduction. The more negative the standard reduction potentials are the better reducing agent the reduction half-reaction will be. In other words, the higher the cathode half-reaction (the more negative) is on the standard reduction table, the better it will be oxidized. It's determined by the standard reduction potentials.

Q20.4.24

Your lab partner wants to recover solid silver from silver chloride by using a 1.0 M solution of HCl and 1 atm H₂ under standard conditions. Will this plan work?

Solution: First you need to determine what is being reduced and oxidized and then write and balance the corresponding half-reactions. Next from those half reactions explain which is the cathode or anode. You can see if this will work by first determining the standard cell potential. You can also verify the spontaneity of the reaction by using the equation that connects the standard reduction potential and the standard Gibbs free energy:

Cathode (Reduced): 2(Ag⁺_(aq) + e^- à Ag_(s)) E^o=0.80V (going from the aqueous silver chloride to the solid silver)

Anode (Oxidation): 2H⁺_(aq) + 2e^- à H_2(g) E^o= 0.00V

E^o_cell= E^o_cathode- E^o_anode

E^o_cell= 0.80-0.00=0.80V

Since E^o_cell is positive, then the reaction will be spontaneous because E^o_cell and ΔG^o are inversely proportional (ΔG^o should be negative).

ΔG^o = -nFE^o_cell n= number of electrons transferred F=Faraday’s Constant= 96,486 C/mol e^-

ΔG^o = -(2 mol e^-)( 96,486 C/mol e^-)(0.80V)= -154377.6V

Yes this is spontaneous and will work.

Q20.9.9

What mass of PbO₂ is reduced when a current of 5.0 A is withdrawn over a period of 2.0h from a lead storage battery?

Solution: The formula n = (I x T)/F I = Current (Amp), T = time (sec), F = 96,486 C/mole e^- , n = # moles of electrons

n = (I x T)/F

n = [(5.0 A)(2 hr)(3600 sec/ 1 hr)]/[(96485 C/mol e^-)]

n = (0.373 mol e^-)/(4 electrons exchanged) = 0.09328 moles

0.09328 moles x [(239.20g)(1 mol)] = 22.31 grams

Mass of PbO₂ = 22.31 grams