H2 Chemistry "Gas Laws" topic
Explanation :
Option 1, increasing the temperature favours the forward
reaction, and therefore with a greater Kc value at the higher
temperature, it means that at equilibrium there would be a greater
number of moles of gas in the equilibrium mixture (ie.
heating favours the thermal decomposition of each N2O4
molecule into two NO2 molecules). Since no. of moles of gas
increases at equilibrium, partial pressure of the equilibrium
gas mixture in the left bulb will experience a larger increase,
compared to smaller increase in the partial pressure of the
nitrogen gas in the right bulb (due to heating), and therefore the
mercury level in the right hand limb will rise.
Option 2, because both LHS and RHS of the equation has the same
number of moles of gas, hence it doesn't matter if the forward
reaction is endo or exo, the no. of moles of gas (in the
left bulb) will remain the same at all temperatures.
(Although partial pressure of the gas in the left
bulb will increase due to heating, bear in mind the
nitrogen gas in the other bulb will also
experience the same increase in partial pressure due to
the heating).
Option 3, "increasing temperature" implies increasing the
temperature of the entire experimental setup, ie. both bulbs.
Hence, partial pressures of both nitrogen gas samples in both bulbs
will increase equally, and the mercury levels remain unchanged in
both limbs.