Consider what happens when a piece of zinc is added to a solution of nitric acid

Question

Consider what happens when a piece of zinc is added to a solution of nitric acid. When the nitric acid reacts with the zinc you see a plume of red smoke. The smoke is produced when the nitrogen monoxide from the first reaction spontaneously reacts with oxygen gas in the air to form the red gas nitrogen dioxide. The reactions for this process are shown below: Reaction 1:3Zn(s) + 8HNO_3(aq) rightarrow 3Zn(NO_3)_2(aq) + 2NO(g) + 4H_2O(g) Reaction 2: 2NO(g) + O_2(g) rightarrow 2NO_2(g) Given that Reaction 1 above is an exothermic reaction, what are the signs of the following thermodynamic parameters for Reaction 1? Delta S_SYS > 0, Delta S_SURR 0 Delta S_SYS > 0, Delta S_SURR > 0, Delta S_Univ > 0 Delta S_SYS

Explanation / Answer

Q22

if the reaction is exothermic, this means it will release heat

so...

The surroundings are being heated, so this must be increasing the entropy of the surorundings, since it is directly propoertional

so dS surr > 0

for the system..

number of moles of gas in products = 2+4 = 6

mles of gas in reactants = 0

this is clearly becoming more chaotic, so the entropy increases in the system

so

dS universe = dSsur + dSSystem

so all increases... then

B is the answer

Q23

for

reaction 2

the reaction is oxidation, meaning it will be eoxthermic

so

dH > 0

the chaos decreases since 3 mol of gas form 2 mol of gas

so

dS < 0

dG = dH - T*dS

dG = + -T*-S = + +

dG is positive

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