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Question:

A spontaneous reaction is impossible if: both ΔH and ΔS are positive; ΔH is negative and ΔS is positive; ΔH is positive and ΔS is negative; both ΔH and ΔS

ΔH is negative and ΔS is positive

ΔH is positive and ΔS is negative

both ΔH and ΔS are positive

both ΔH and ΔS

Solution:

A spontaneous reaction is impossible if ΔH is positive and ΔS is negative as it will lead to a positive value of ΔG. For a reaction to be non-spontaneous, ΔG should be positive. Note: When ΔH is positive and ΔS is negative, ΔG = ΔH - TΔS; ΔG = positive - T × negative; ΔG = positive + positive; ΔG = positive