Multiple Choice
For a reaction to be spontaneous at all temperatures, the signs of ΔH and ΔS must be:
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19. Chemical Thermodynamics
Spontaneous vs Nonspontaneous Reactions
Multiple Choice
Which of the following pairs of reactants will result in a spontaneous redox reaction at 25°C?
A
Fe³⁺(aq) + Zn(s)
B
Ag⁺(aq) + Cu(s)
C
Cr³⁺(aq) + Sn(s)
D
Pb²⁺(aq) + Fe(s)
Verified step by step guidance1
Identify the standard reduction potentials for each half-reaction involved in the given pairs of reactants. You can find these values in a standard reduction potential table.
For each pair, write the half-reactions and their corresponding standard reduction potentials. For example, for Fe³⁺(aq) + Zn(s), write the reduction half-reaction for Fe³⁺ and the oxidation half-reaction for Zn.
Calculate the standard cell potential (E°cell) for each pair by using the formula: E°cell = E°cathode - E°anode. The cathode is where reduction occurs, and the anode is where oxidation occurs.
Determine the spontaneity of the reaction by evaluating the sign of E°cell. A positive E°cell indicates a spontaneous reaction, while a negative E°cell indicates a non-spontaneous reaction.
Compare the calculated E°cell values for all pairs and identify which pair has a positive E°cell, indicating a spontaneous redox reaction at 25°C.
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