Which one of the following combinations of reagents will result in a spontaneous reaction?
A) Al(s) + CuCl2(aq)
B) Al(s) + CaCl2(aq)
C) Zn(s) + CaCl2(aq)
D) Cu(s) + ZnCl2(aq)
I know the answer is A, but what I don't know is why, or how to figure this out. Thanks!
Look at the activity series of metals.
A metal will displace an ION below it in the activity series. And that is a spontaneous reaction.
http://www.files.chem.vt.edu/RVGS/ACT/notes/activity_series.html
For example, Zn metal will displace Cu^+2 ion in the reaction
Zn + CuCl2 ==> Cu + ZnCl2
But a metal will NOT displace the ION of a metal above it in the activity series.
CuCl2 + Zn ==> no reaction.
To figure out which combination of reagents will result in a spontaneous reaction, we need to consider the reactivity of the metals involved. In general, metals tend to react with metal cations in solution based on their relative positions in the activity series.
The activity series of metals arranges them in decreasing order of their reactivity. A more reactive metal can displace a less reactive metal from its salt solution. Here's how you can figure out the answer:
1. First, locate the metals used in each combination - Al, Cu, Zn.
2. Look up the activity series of metals to compare their reactivity. In the activity series, metals higher up are more reactive and can displace metals below them.
3. Comparing Al, Cu, and Zn, you'll find that Al is more reactive than Cu and Zn. Specifically, the activity series usually places Al above both Cu and Zn.
4. Now, consider the given combinations and check if the metals involved in each combination follow the reactivity pattern. Let's go through each option given:
A) Al(s) + CuCl2(aq): Al is more reactive than Cu. Therefore, Al can displace Cu from its salt CuCl2, resulting in a spontaneous reaction.
B) Al(s) + CaCl2(aq): This combination involves Al and Ca. Although Al is more reactive than Ca, it cannot displace Ca from its salt CaCl2. Therefore, the reaction will not be spontaneous.
C) Zn(s) + CaCl2(aq): Zn is lower in the activity series than Ca. Therefore, Zn cannot displace Ca from its salt CaCl2. So, this reaction will not be spontaneous.
D) Cu(s) + ZnCl2(aq): Cu is less reactive than Zn. Hence, Cu cannot displace Zn from its salt ZnCl2, and the reaction will not be spontaneous.
Based on these explanations, only combination A) Al(s) + CuCl2(aq) will result in a spontaneous reaction because Al is more reactive than Cu.