Hi Angel. A great question. A redox couple assumes one reduction and one oxidation and a positive reduction potential. So what we need to do is to switch one of the half reactions and the corresponding sign (+ or -) and then sum them to give a positive number. This will involve switching the one that has a lower standard reduction potential (which is higher on the list). For example, if we build a cell using magnesium and copper, how do we know which one to change. Magnesium is higher than copper in our table. Mg2+ + 2e- Mg(s) -2.36V while Cu2+ + 2e- Cu(s) 0.34V. If we change the copper, both half reactions are negative which will give us a negative value which is not spontaneous (won't produce a voltage). However if we reverse the magnesium equation Mg(s) Mg2+ + 2e- and change the sign +2.36V then when we add the two together we get (2.36 + 0.34 = 2.70V). This gives us a positive value and hence a spontaneous reaction which can generate a voltage if set up in a galvanic cell. It also explain why solid magnesium will displace coppoer ions from a solution but solid copper will not displace magenisum ions form a solution. I hope that helps!
thank you!
how do you know which half reaction to change in oxidation
Hi Angel. A great question. A redox couple assumes one reduction and one oxidation and a positive reduction potential. So what we need to do is to switch one of the half reactions and the corresponding sign (+ or -) and then sum them to give a positive number. This will involve switching the one that has a lower standard reduction potential (which is higher on the list). For example, if we build a cell using magnesium and copper, how do we know which one to change. Magnesium is higher than copper in our table. Mg2+ + 2e- Mg(s) -2.36V while Cu2+ + 2e- Cu(s) 0.34V. If we change the copper, both half reactions are negative which will give us a negative value which is not spontaneous (won't produce a voltage). However if we reverse the magnesium equation Mg(s) Mg2+ + 2e- and change the sign +2.36V then when we add the two together we get (2.36 + 0.34 = 2.70V). This gives us a positive value and hence a spontaneous reaction which can generate a voltage if set up in a galvanic cell. It also explain why solid magnesium will displace coppoer ions from a solution but solid copper will not displace magenisum ions form a solution. I hope that helps!
@@DocHarrison thanks
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