Chemistry

36. Out of diamond and graphite, which has greater entropy? At what temperature entropy of a substance is zero?

Expansion of a gas in vacuum is called free expansion. Calculate the work done and the change in internal energy when 1 litre of ideal gas expands isothermally into vacuum until its total volume is 5 litre?

36. Out of diamond and graphite, which has greater entropy? At what temperature entropy of a substance is zero?

35. What is the enthalpy of formation of the most stable form of an element in its standard state?

34. When is bond energy equal to bond dissociation energy?

33. Which one is the correct unit for entropy?

(a) KJ mol                   

(b) JK mol

(c) JK mol^-1                      

(d) KJ mol^-1

3. The enthalpies of all elements in their standard states are:                       

(i) Unity                   

(ii) Zero

(iii) < 0                     

(iv) Different for each element

2. For the process to occur under adiabatic conditions, the correct condition is:

(i) ?T= 0                           

(ii) ?p = 0

(iii) q = 0                           

(iv) w = 0   

896 mL vapour of a hydrocarbon 'A' having carbon 87.80% and hydrogen 12.19% weighs 3.28g at STP. Hydrogenation of 'A' gives 2-methylpentane. Also 'A' on hydration in the presence of H₂SO₄ and HgSO₄ gives a ketone 'B' having molecular formula C₆H₁₂O. The ketone 'B' gives a positive iodoform test. Find the structure of 'A' and give the reactions involved.

An alkyl halide C₅H₁₁Br (A) reacts with ethanolic KOH to give an alkene 'B', which reacts with Br₂ to give a compound 'C', which on dehydrobromination gives an alkyne 'D'. On treatment with sodium metal in liquid ammonia one mole of 'D' gives one mole of the sodium salt of 'D' and half a mole of hydrogen gas. Complete hydrogenation of 'D' yields a straight chain alkane. Identify A,B, C and D. Give the reactions invovled.