How do I do this question step by step?

You need to pick up the true statement. With reaction D statement given is not true. Only reaction A statement give is true and rest all are incorrect explanations are not true.

To check which combinations of reactions will give ∆G negative that will be the spontaneous reaction.

QuoteIs it okay if the first equation has negative entropy? shouldn't one of them be favourable and the other one non favourable?

Only ∆S will not decide whether the reaction is spontaneous or not. We need to consider ∆H also and combination of both factors are included in ∆G equation.
Like formation of ethyne
You need to divide first equation by half and add it in second equation to get the desired reaction of formation of ethyne. Same mathematical operations you will do it on ∆G values and then add them. Now check if final ∆G is negative or positive. If positive then then non spontaneous and coupling is not helping us and if negative then coupling will help in making it spontaneous.
In other options check adding these reactions are giving ∆G negative or not. If yes coupling is helping otherwise not.
Extraction of solid Cu from Cu₂S is feasible only if you couple both reactions.
Formation of N₂H₄ is non spontaneous in option 1 (∆G negative for first reaction which is formation reaction).Now if I couple it with any of other two reactions given still ∆G will be positive so this is the answer in which coupling is not making it spontaneous.
In all rest ∆G is negative on adding reactions.

okay all that is not needed here in this question above.

Quote from: uma on April 15, 2024, 06:50:07 PMIt gets the sparkfrom collisions among the molecules that is the reason we dont have H2 gas in the atmosphere and that is the reason we are still working how to make a battery of H2 and O2.

But only if the activation energy is high enough. In the atmosphere there is no H2, because there is no reaction to develop any. H2 is mainly man made by electrolysis or oil cracking refinery.

In comparison flourine and hydrogen ignites directly if mixed.

By using chlorine it needs a light Flash, in a darf room also nothing happens.

By using oxygen a spark , flame or also light Flash can ignite it.

Its because of different activation energy needed.

It gets the sparkfrom collisions among the molecules that is the reason we dont have H2 gas in the atmosphere and that is the reason we are still working how to make a battery of H2 and O2.

Quote from: uma on April 15, 2024, 09:27:48 AM2H2(g) + O2(g) ----> 2H2O (g)
It is a combustion reaction so enthalpy change is negative.Entropy change is also negative as number of gaseous moles are decreasing from reactants to products.
This reaction is very spontaneous at low temperature becuase H2 (g) is very reactive and immediately undergoes oxidation even at low temperature.This means Gibb's free energy is negative for this reaction.25 degree C is low temperature for DG to be negative.This reaction is very spontaneous even at romm temperature and reason is reactivity of hydrogen gas.

But it need still a spark or flash. You can mix hydrogen and oxygen, without a spontanous reaction.

If salt bridge is replaced by Pt metal then solutions of anode and cathode compartments will not get anions and cations to neutralize the solutions.
Reaction will stop immediately in the absence of salt bridge.and hence voltage will be zero.

First thing you need to pick up answer from given options.
And 2000K this reaction has dG is negative,
dG = dH -TdS.
dS is negative so reaction is spontaneous at low temperature.

T< dH/dS. = 803/0.005 K
2000Kis less than calculated above.

Why will the voltage be 0?