11.
If enthalpies of formation of $${C_2}{H_4}\left( g \right),C{O_2}\left( g \right)$$ and $${H_2}O\left( l \right)$$ at $${25^ \circ }C$$ and $$1\,atm$$ pressure are $$52,-394$$ and $$ - 286\,kJ/mol,$$ the enthalpy of
combustion of ethene is equal to
12.
When $$1\,mole$$ gas is heated at constant volume, temperature is raised from 298 to 308$$\,K.$$ Heat supplied to the gas is 500$$\,J.$$ Then, which statement is correct?
$$\eqalign{
& {\text{We}}\,\,{\text{know that,}}\,\,\Delta H = \Delta E + p\Delta V \cr
& {\text{When,}}\,\,\Delta V = 0 \cr
& \therefore \,\,\Delta H = \Delta E \cr} $$
From first law of thermodynamics $$\Delta E = q - W$$
$$\eqalign{
& {\text{In given problem}}\,\,\Delta H = 500\,J \cr
& - W = - p\Delta V,\,\Delta V = 0 \cr
& {\text{so,}}\,\Delta E = q = 500\,J \cr} $$
13.
An ideal gas expands against a constant external pressure of 2.0 atmosphere from 20
litre to 40 litre and absorbs $$10\,kJ$$ of heat from surrounding. What is the change in internal energy of the system?
$$\left( {{\text{given}}:1\,atm - litre = 101.3\,J} \right)$$
$$\Delta H = \Delta E + P\Delta V,$$ for solid and liquid, $$\Delta V = 0$$
or $$\Delta H = \Delta E + \Delta nRT,$$ for solids and liquids $$\Delta n = 0$$
15.
Consider the following reaction :
$$C{O_{\left( g \right)}} + \frac{1}{2}{O_{2\left( g \right)}} \to C{O_{2\left( g \right)}}$$
How are $$\Delta U$$ and $$\Delta H$$ related for the reaction ?
Spontaneity of reaction depends on tendency to acquire minimum energy state and maximum randomness. For a spontaneous process in an isolated system the change in entropy is positive.
17.
Given
$$\eqalign{
& {C_{\left( {{\text{graphite}}} \right)}} + {O_2}\left( g \right) \to C{O_2}\left( g \right);\,\,\,\,\,{\Delta _r}{H^ \circ } = - 393.5\,kJ\,mo{l^{ - 1}} \cr
& {H_2}\left( g \right) + \frac{1}{2}{O_2}\left( g \right) \to {H_2}O\left( {\text{l}} \right);\,\,\,{\Delta _r}{H^ \circ } = - 285.8\,kJ\,mo{l^{ - 1}} \cr
& C{O_2}\left( g \right) + 2{H_2}O\left( {\text{l}} \right) \to C{H_4}\left( g \right) + 2{O_2}\left( g \right);\,{\Delta _r}{H^ \circ } = + 890.3\,kJ\,mo{l^{ - 1}} \cr} $$
Based on the above thermochemical equations, the value of $${\Delta _r}{H^ \circ }$$ at $$298 K$$ for the reaction
$${C_{\left( {{\text{graphite}}} \right)}} + 2{H_2}\left( g \right) \to C{H_4}\left( g \right)$$ will be :
18.
If the enthalpy change for the transition of liquid water to steam is $$30\,kJ\,mo{l^{ - 1}}$$ at $${27^ \circ }C,$$ the entropy change for the process would be
19.
Given that bond energies of $$H-H$$ and $$Cl-Cl$$ are $$430\,kJ\,mo{l^{ - 1}}$$ and $$240\,kJ\,mo{l^{ - 1}}$$ respectively and $$\Delta {H_f}$$ for $$HCl$$ is $$ - 90\,kJ\,mo{l^{ - 1}}.$$ Bond enthalpy of $$HCl$$ is
20.
In conversion of lime-stone to lime,
$$CaC{O_3}\left( s \right) \to CaO\left( s \right) + C{O_2}\left( g \right)$$ the values of $$\Delta {H^ \circ }$$ and $$\Delta {S^ \circ }$$ are $$ + 179.1\,kJ\,mo{l^{ - 1}}$$ and $$160.2\,J/K$$ respectively at $$298 K$$ and 1bar. Assuming that $$\Delta {H^ \circ }$$ and $$\Delta {S^ \circ }$$ do not change with temperature, temperature above which conversion of limestone to lime will be spontaneous is