GOB Chemistry

Learn the toughest concepts covered in your GOB - General, Organic, and Biological Chemistry class with step-by-step video tutorials and practice problems.

Classification & Balancing of Chemical Reactions

Spontaneous Redox Reactions

Spontaneous Redox Reactions occur when an element displaces another element within a compound. 

Activity Series Chart



Spontaneous Redox Reactions Concept 1

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redox reactions are spontaneous. When an element can successfully displace another element within a compound and when we say the term displace that means to remove an element from its compound and thereby reducing it. So to displace an element means I'm actually reducing that element And we're gonna say here, we utilize what's called an activity series chart to determine if an element can displace another element. Now, what we're gonna say here is we're gonna see an element that is higher in the activity series, will displace an element lower in the activity series chart. And what we need to also remember is that recall an oxidizing agent is reduced and a reducing agent will be oxidized. So if we take a look here at this activity series chart, we have lithium potassium calcium all the way down to gold down here. And what we can say here is up near lithium, that's where we have the strongest reducing agent, which means that we have the greatest propensity for oxidation. So we want to be oxidized a lot. And up here is where we have the weakest by default, the weakest oxidizing agent, which means reduction does not want to happen up here. Okay, so we're gonna say at this end of the activity series chart, this is the greatest tendency to lose electrons. If we do the opposite end. Down here we have the weakest reducing agent, which means that we have the least likely to be oxidized. Oxidation is very weak here, oxidation. Uh huh. And down here we have the strongest oxidizing agent, which means reduction really wants to happen down here. So down here on the activity series charges where we have the greatest tendency to gain electrons. So just remember when looking at this activity series chart an element that's higher up will displace another element that's below it. So if we had sodium it could displace zinc from another compound. Why? Because sodium is higher up than zinc is


Spontaneous Redox Reactions Example 1

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based on the activity series chart determined the following reaction represents a spontaneous redox reaction basically. We're looking to see can this calcium displace this silver? And we know that we're trying to compare those two because there are the two elements on the activity series chart up above. Now take a look. Is calcium higher up than silver. If it is then we can successfully displace the silver, basically kick it out. So if you look calcium is indeed higher up. Right? So step one, we locate the mono atomic element on the activity series chart, we find out where both are located. And remember step two. If it is higher on the activity series chart, it will displace the element within the nearby compound. So silver is gonna get kicked out. Medals by themselves exist as solids at room temperature except for mercury. Plus now calcium and chlorine are going to combine together to give us our new ionic compound. Remember calcium is in Group Two way, so it's two plus for its charge Chlorine and groups 70. So it's -1. We crisscrossed the numbers to give us our ionic compound Which would come out to BCACL two. And here we can make it a solid if we want. The state's really are not that important. What's important is that calcium can successfully display silver within this um redox reaction and as a result it is spontaneous. Now if we wanted to balance this, we'd say we have to chlorine is here and only one here. So I put it to here and then as a consequence, I also have to put a two here for this silver. So these will be our coefficients for a balanced redox reaction. one, as the coefficients.

Which element is the best reducing agent?


Determine whether which of the following redox reactions will occur spontaneously in the forward direction?

a) Ni(s) + Zn2+(aq) → Ni2+(aq) + Zn(s)
b) Fe(s) + Pb4+(aq) →   Fe2+(aq) + Pb(s)
c) Al(s) + Ag+(aq) →  Al3+(aq) + Ag(s)
d) Pb(s) + Mn2+ (aq) → Pb2+(aq) + Mn(s)


Suppose you wanted to cause Ni2+ ions to come out of solution as solid Ni. Which metal could you use to accomplish this?