Problem 83 - Introductory Chemistry Atoms First

Question

Lithium is a very active metal, so active that it reacts with water to make flammable hydrogen gas. \(\mathrm{Li}(s)+\mathrm{H}_{2} \mathrm{O}(l) \rightarrow \mathrm{LiOH}(s)+1 / 2 \mathrm{H}_{2}(g)\) (a) What metal would you use in combination with Li to make a battery having the highest voltage? (Consult the EMF series.) (b) Too rapid a discharge of a lithium battery (which can occur if there is a short circuit) can overheat a lithium battery and cause it to explode and catch fire. Why is trying to put out such a fire with water a bad idea? (c) Would lithium be the anode or cathode in a lithium ion battery? Explain.

Step-by-Step Solution

Answer

In summary: (a) Pairing lithium with fluorine would produce the highest voltage battery, as they have the largest difference in standard electrode potentials according to the EMF series. (b) Using water to put out a lithium battery fire is a bad idea because lithium reacts with water to release flammable hydrogen gas, further fueling the fire. Instead, use a class D fire extinguisher or dry sand. (c) In a lithium-ion battery, lithium would function as the anode, as it readily loses its valence electron to become a positively charged lithium ion, releasing cations and electrons during discharge.

Step 1: (a) Consult the EMF series to find the metal for the highest voltage battery with Li

To determine which metal would produce the highest voltage when combined with lithium in a battery, consult the Electromotive Force (EMF) series. The greater the difference in standard electrode potentials between two metals, the higher the voltage the battery composed of these two metals would yield. From the EMF series, we can see that Lithium (Li) has a standard electrode potential of \( -3.04 V\) and Fluorine (F) has a potential of \( 2.87V\). The difference between these two potentials is the largest, so pairing lithium with fluorine would produce the highest voltage battery.

Step 2: (b) Explain why using water to put out a lithium battery fire is a bad idea

Using water to extinguish a lithium battery fire is not a good idea because lithium reacts with water to release hydrogen gas, as given in the chemical equation: \(\mathrm{Li}(s)+\mathrm{H}_{2} \mathrm{O}(l) \rightarrow \mathrm{LiOH}(s)+1 / 2 \mathrm{H}_{2}(g)\) As hydrogen gas is flammable, the reaction would generate more heat and fuel the fire instead of extinguishing it. In order to extinguish a lithium battery fire, it is recommended to use a class D fire extinguisher or dry sand instead of water.

Step 3: (c) Determine if lithium would be the anode or cathode in a lithium-ion battery and explain

In a lithium-ion battery, lithium would function as the anode. This is because the role of the anode is to release positively charged ions (cations) and electrons during discharge. Lithium, being a highly reactive metal, readily loses its valence electron to become a positively charged lithium ion. The reaction occurring at the anode during discharge can be represented as: \(\mathrm{Li}(s) \rightarrow \mathrm{Li}^{+}(aq) + e^{-}\) By releasing positively charged lithium ions and electrons, the lithium electrode functions as the anode in a lithium-ion battery.

Key Concepts

Electromotive Force (EMF) Series

Understanding the Electromotive Force (EMF) series is crucial when determining which metals to pair in a battery to optimize its voltage. The EMF series ranks elements based on their standard electrode potentials. These are measured in volts and indicate a substance's ability to be reduced or oxidized. To create a battery with the highest voltage, two metals with a substantial difference in electrode potentials should be selected. For example, lithium, with a potential of -3.04 V, and fluorine, with a potential of 2.87 V, exhibit the largest difference when compared, resulting in a high-voltage battery due to this substantial gap. In essence, the higher the difference between the two potentials, the greater the battery's output voltage.

Anode and Cathode in Batteries

In any battery, the anode and cathode play essential roles. These parts are responsible for electron flow and determine the direction of current. The basic rule is that oxidation occurs at the anode, and reduction occurs at the cathode. In the context of a lithium-ion battery, lithium serves as the anode. This is because it undergoes oxidation, releasing electrons and lithium ions upon discharge.

The equation representing this process is:

• Oxidation at the anode: \(\mathrm{Li}(s) ightarrow \mathrm{Li}^{+}(aq) + e^{-}\)

During the battery's operation, the electrons flow towards the cathode through an external circuit, while lithium ions traverse the electrolyte. The dual movement is the battery's essential mechanism to provide power.

Lithium Reactions with Water

Lithium's reactivity with water is notable and hazardous. The reaction between lithium and water results in the formation of lithium hydroxide and hydrogen gas. The chemical equation for this reaction is: \(\mathrm{Li}(s) + \mathrm{H}_{2} \mathrm{O}(l) \rightarrow \mathrm{LiOH}(s) + 1/2 \mathrm{H}_{2}(g)\) .

The generation of hydrogen gas is particularly concerning because it is highly flammable. If lithium comes into contact with water, the release of hydrogen could potentially fuel a fire rather than extinguishing it. This sweet yet fierce reaction showcases why water is unsuitable for controlling lithium battery fires. Always ensure appropriate measures, like using a class D fire extinguisher, are taken in such cases.

Fire Safety and Chemical Reactions

When dealing with lithium battery fires, safety is paramount. As discussed, attempting to quench such a fire with water is ill-advised due to the vigorous reaction that produces explosive hydrogen gas. Instead, using a class D fire extinguisher designed for metal fires is recommended.

Alternative methods involve smothering the fire with materials like dry sand to cut off the fire's oxygen supply. Additionally, understanding the chemical nature of lithium aids in these safety considerations. Staying knowledgeable about correct extinguishing methods can prevent a manageable situation from escalating into a dangerous fire hazard. Therefore, knowing the interaction between chemicals used in everyday devices is as integral to safety as the devices themselves.