Select which of the following standard enthalpy of formation values is not zero at 25∘C: Na(s) CH4(g) H(g) Hg(l) Ne(g) S8(rhombic)

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Select which of the following standard enthalpy of formation values is not zero at 25∘C:   Na(s)    CH4(g)   H(g)   Hg(l)   Ne(g)   S8(rhombic)

soanooooo40 · Accepted Answer

Step 1  Those whose standard enthalpy of formation values is not zero at 25∘C are to be selected:  aNa(s)bCH4(g)cH(g)dHg(l)eNe(g)fS8(rhombic)  Step 2 The standard enthalpy of formation is the change in enthalpy when 1 mole of substance in the standard state is formed from its pure elements under the same conditions.  The standard enthalpy of formation of a pure element in its reference form is zero. For example, the standard of formation of Carbon in graphite form is zero.  Step 3  a. Na (s)-The standard form of sodium is in solid state. Therefore, △Hfo(Na,s)=0  b. CH4(g) - It is not a pure element. Therefore, △Hfo(CH4,g) is not 0.  c. H(g) - The standard form of H is H2(g). Therefore, △Hfo(H,g) is not 0.  Step 4  d. Hg(l) The standard state of mercury is in liquid form. Therefore, △Hfo(Hg,l)=0  e. Ne(g) - Neon exists in gaseous standard state. Therefore, △Hfo(Ne,g)=0  f. S8(Rhombic) - sulfur exists in rhombic standard state. Therefore, △Hfo(S8,ρmbic)=0  Step 5  Hence, the standard enthalpy of formation values for CH4(g) and H(g) is not zero at 25∘C.

puhnut1m · Accepted Answer

Only two elements CH4 and S8 (monoclinic) .   −74.9kjmol for CH4, due to stable and favorable bond formation   S8 has an enthalpy value of 30 Kj per mole because there is some weak bonding as crystals are forming in the monoclinic crystal structure

alenahelenash · Accepted Answer

There are three correct options for the following questions. The correct answer is methane, S8(monoclinic), and H(g). These three compounds have a non-zero value of enthalpy of formation.

Select which of the following standard enthalpy of formation values

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