Acetic acid forms a dimer in the gas phase:

The dimer is held together by two hydrogen bonds with a total strength of $66.5 \mathrm{kJ}$ per mole of the dimer. At $25°\mathrm{C}$, the equilibrium constant for the dimerisation is $1.3\times {10}^3$ (pressure in $\mathrm{atm}$). What is ${\mathrm{\Delta S}}^{\circ }$ for the reaction? Assume that $\mathrm{\Delta H}$ does not vary with temperature.

When $12 \mathrm{g}$ of carbon reacted with oxygen to form $\mathrm{CO}$ and ${\mathrm{CO}}_2$ at $25 °\mathrm{C}$ and constant pressure, $75 \mathrm{kcal}$ of heat was liberated and no carbon remained. Calculate the mass of oxygen that reacted. Given,

$\begin{array}{l}\mathrm{C}+{\mathrm{O}}_2⟶{\mathrm{CO}}_2; \mathrm{\Delta H}=-94.05 \mathrm{kcal} {\mathrm{mole}}^{-1}\\ \mathrm{C}+\frac{1}{2}{\mathrm{O}}_2⟶\mathrm{CO}; \mathrm{\Delta H}=-26.41 \mathrm{kcal} {\mathrm{mole}}^{-1}\end{array}$

Answer correct up to one place of decimal.

Assuming that $50\%$ of the heat is useful, how many $\mathrm{kgs}$ of water, at $15°\mathrm{C}$, can be heated to $95°\mathrm{C}$ by burning $200 \mathrm{litres}$ of methane at $\mathrm{NTP}? {\mathrm{\Delta H}}_{\text{combustion }}\left({\mathrm{CH}}_4\right)$ $=211 \mathrm{kcal}/\mathrm{mole},\text{ specific heat of water }=1 \mathrm{kcal}/\mathrm{kg} \mathrm{K}.$

Answer after rounding off to the nearest integer value.

The thermochemical equation for the dissociation of hydrogen gas into atoms may be written as

${\mathrm{H}}_2\to 2\mathrm{H}; \mathrm{\Delta H}=436 \mathrm{kJ}$

What is the ratio of the energy yield on combustion of hydrogen atoms to steam to the yield on combustion of an equal mass of hydrogen molecules to steam? ${\mathrm{\Delta H}}_{\text{combustion }}\text{ for }{\mathrm{H}}_2=-241.81 \mathrm{kJ}$

Answer correct up to one significant value.

Calculate the value of $\log {\mathrm{K}}_{\mathrm{p}}$ for the reaction: ${\mathrm{N}}_2\left(\mathrm{g}\right)+3{\mathrm{H}}_2\left(\mathrm{g}\right)\rightleftharpoons 2{\mathrm{NH}}_3\left(\mathrm{g}\right)$ at $25°\mathrm{C}$. The standard enthalpy of formation of ${\mathrm{NH}}_3\left(\mathrm{g}\right)$ is $-46 \mathrm{kJ}$ and the standard entropies of ${\mathrm{N}}_2, {\mathrm{H}}_2$ and ${\mathrm{NH}}_3$ gases are $191, 130, 192 {\mathrm{JK}}^{-1} {\mathrm{mol}}^{-1}$, respectively. 

Round off your answer to the nearest integer.

In a fuel cell, methanol is used as a fuel and oxygen gas is used as an oxidizer. The reaction is ${\mathrm{CH}}_3\mathrm{OH}\left(\mathrm{l}\right)+\frac{3}{2}{\mathrm{O}}_2\left(\mathrm{g}\right)\to {\mathrm{CO}}_2\left(\mathrm{g}\right)+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$.

At $298 \mathrm{K}$, the standard Gibbs energies of the formation for ${\mathrm{CH}}_3\mathrm{OH}\left(\mathrm{l}\right), {\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$ and ${\mathrm{CO}}_2\left(\mathrm{g}\right)$ are $-166.2,-237.2$ and $-394.4 \mathrm{kJ} {\mathrm{mol}}^{-1}$, respectively. If the standard enthalpy of combustion of methanol is $-726 \mathrm{kJ} {\mathrm{mol}}^{-1}$, the efficiency of the fuel cell will be: