An electric device delivers a current of [tex]$15.0 A$[/tex] for 30 seconds. How many electrons flow through it?
Answer (2)
Lithium is more reactive than calcium.
Lithium will displace calcium from calcium bromide solution.
The balanced chemical equation is 2 L i ( s ) + C a B r 2 ( a q ) → C a ( s ) + 2 L i B r ( a q ) .
The correct equation that predicts the products of the reaction is 2 L i ( s ) + C a B r 2 \t ( a q ) → C a ( s ) + 2 L i B r ( aq ) .
Explanation
Problem Analysis We are given a single replacement reaction between solid lithium (Li) and a solution of calcium bromide ( C a B r 2 ). We need to determine which element, lithium or calcium, is more reactive and identify the correct balanced chemical equation for the reaction.
Determining Relative Reactivity The activity series of metals ranks metals in order of their reactivity. A more reactive metal will displace a less reactive metal from its compounds in a single replacement reaction. Lithium (Li) is higher in the activity series than calcium (Ca), indicating that lithium is more reactive.
Predicting the Products Since lithium is more reactive than calcium, it will displace calcium from the calcium bromide solution. This means lithium will combine with bromine to form lithium bromide ( L i B r ), and calcium will be released as a solid ( C a ).
Writing the Balanced Equation The balanced chemical equation for this reaction is: 2 L i ( s ) + C a B r 2 ( a q ) → C a ( s ) + 2 L i B r ( a q ) This equation shows that two moles of solid lithium react with one mole of calcium bromide in aqueous solution to produce one mole of solid calcium and two moles of lithium bromide in aqueous solution.
Identifying the Correct Equation Comparing the predicted equation with the given options, we find that option iii matches the correct balanced equation. Therefore, the correct equation is: 2 L i ( s ) + C a B r 2 ( a q ) → C a ( s ) + 2 L i B r ( a q )
Final Answer In summary, lithium is more reactive than calcium, and the correct balanced chemical equation for the reaction is: 2 L i ( s ) + C a B r 2 ( a q ) → C a ( s ) + 2 L i B r ( a q )
Examples
Single replacement reactions are commonly used in various industrial processes, such as the extraction of metals from their ores. For instance, a more reactive metal like zinc can be used to extract copper from copper sulfate solution. This principle is also applied in batteries, where the flow of electrons from a more reactive metal to a less reactive metal generates electricity. Understanding the activity series and single replacement reactions helps in designing efficient extraction methods and developing new battery technologies.
By using the current value and the duration the current flows, we calculate the total charge delivered. This charge is then divided by the charge of a single electron to find the total number of electrons, which is approximately 2.81 x 10²¹ electrons. Thus, 2.81 x 10²¹ electrons flow through the device in 30 seconds.
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