Use bond dissociation energies to estimate the value of delta H for the followin
ID: 1002305 • Letter: U
Question
Use bond dissociation energies to estimate the value of delta H for the following reaction: CH_4(g) + Cl_2(g) rightarrow CH_3Cl(g) + HCl(g) -109 kJ +109 kJ +301 kJ -301 kJ A particular reaction has the following values at 30.0 degree C: delta H = 25.0 kJ and delta S = 138.0 J/K. Calculate the value of delta G and determine if the reaction is spontaneous or nonspontaneous at this temperature. delta G = The reaction is spontaneous or nonspontaneous. (circle one) Which one of the following has ONLY disperson forces? HCl CH_3OH CH_4 H_2S Which of the following arranges the compounds in order of increasing molecular polarity? CH_4Explanation / Answer
34) This problem is based on Gibbs free energy change for a reaction.
Gibbs equation is,
G = H – TS
Where G = Gibbs energy change for reaction.
Given:
T = 30 oC = 30 + 273 = 303 K
H = + 25.0 kJ = 25000 J
S = +138.0 J/K
Substitute these values in Gibbs equation and calculate G = ?
G = 25000 – 303 x 138.0
G = 25000 – 41814
G = – 16814
G = – 16.814 kJ
Gibbs free energy change for the given reaction is – 16.814 kJ.
G is negative and hence reaction is spontaneous.
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35)
In non-polar molecules molecular association is through only London forces or dispersive forces.
Among given molecules only Methane is a non-polar molecule and hence in Methane (CH4) only London forces are present.
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36) As electronegativity of 2 bonded atoms increases polarity in bond and in molecule as a whole increase.
CH4 is a non-polar molecule i.e. having 0 dipole moment.
Among Halomethane (Haloalkanes)
Increasing order of electronegativity is Br < Cl < F.
Hence increasing order of polarity is H3C-Br < H3C-Cl < H3C-F.
Finally Increasing order of molecular polarity is,
H4C < H3C-Br < H3C-Cl < H3C-F.
Answer option: (d).
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37)
Exothermic reactions: Reactions in which heat energy is evolved out is called as an exothermic reaction.
According to Le Chatelier’s principle low temperature favors the forward exothermic reaction.
Hence fist statement that,
Exothermic reactions are faster at lower temperature than at high temperature.
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