Predicting if a reaction will occur?

Question

Please help me figure out if these reactions will occur!

Note: This is not my homework..but it is examples as to how to see how to do my homework.

Mg(s)+CuCl2(aq)-->
Pb(NO3)2(aq)+Zn(s)-->
KI(aq)+Cl2(g)-->
Cu(s)+FeSo4(aq)-->

Please help me understand how a reaction will occur.

Thanks so much!

Answer 1

Cassandra C has given you a very good answer.
You are interested in a single type of reaction: single displacement. It is a redox reaction so you have to think which compound is more happy having extra electrons (more electronegative).

In the case of A+BX-> AX + B, B(+) in BX is a cation and is missing an electron. If B is a more electronegative negative element than A, then it will steal away the electron from A and the reaction will occur. If A is more electronegative then B is not "strong" enough to steal the electron and the reaction will mot occur.

In the case of Y+BX -> BY+X you have the opposite. X(-) in BX has already an extra electron. So if X is more electronegative than Y it will not give away the electron and the reaction will not occur.

This is an oversimplified reasoning. The proper one is that you have to look at the standard reduction potentials (E0) which give the reactivity series. The half-reaction with the highest reduction potential will be the one favoured or more correctly the reaction will occur if the redox potential of the whole reaction is positive.

For instance you can find a detailed table at
http://www.northland.cc.mn.us/Chemistry/standard_reduction_potentials.htm

Let's see your reaction
Cu+FeSO4 -> CuSO4+ Fe
In this case the half reactions would be
Cu - 2e -> Cu(+2)
Fe(+2) +2e-> Fe

From the website we get that for
Cu(+2) + 2e->Cu E01=+0.342 Volt
Fe(+2) +2e-> Fe E02=-0.447 Volt

E01 is more positive than E02 thus Cu(+2) tends to get electrons from Fe and not the other way around so the reaction will not occur
OR
You find the E of the reaction like this.
The second half-reaction is in the form we want it. The first is in the reverse. So we just reverse the reaction and the sign for the potential

Cu -> Cu(+2) +2e E01'=-0.342
Fe(+2) +2e-> Fe E02=-0.447 and add

Cu + Fe(+2)+2e -> Cu(+2)+ Fe+ 2e with E=E01'+E02= -0.342+(-0.447)

Therefore Cu+Fe(+2) -> Cu(+2) + Fe E= -0.789<0 and so the reaction will not occur.

Answer 2

Mg(s) + CuCl2 (aq) --> MgCl2(aq) + Cu(s)
Pb(NO3)2(aq) + Zn(s)--> Zn(NO3)2(aq) + Pb(s)
2KI(aq) + Cl2(g) --> 2KCl(aq) + I2 (l)
Cu(s)+FeSO4(aq)---> no reaction

If I'm not wrong, u'll have to see the oxidation/reduction property (reactivity) of the element...

Answer 3

when deciding the reaction, the most important thing to look for in substitution reaction ( like what you have examples of) is to decide if the element that you are using to replace the other element is more electronegative than the other one. For example

2 NaCl + H2 ------> does not become NaH + Cl2

the electronegative trend goes up and towards the right,


Don't forget to balance your equations.

Good Luck,

Answer 4

Mg(s)+ CuCl2(aq)---->MgCl(aq) + Cu2
Cu(s) + FeSO4 (aq)---->Cu2SO4 (aq)+ Fe(s)
thas the littel help i can offer.