UPSC Chemistry PYQs 2015 | Vaidra

1Medium10 marks

An important metabolic step is the conversion of fumarate to malate : Fumarate(aq) <=> Malate(aq). At 25 °C, the equilibrium constant for the reaction, K = a_m / a_f = 4, where a_f is the activity of fumarate and a_m is the activity of malate.

(i) Calculate the standard Gibbs energy change, Delta G^o, for the above reaction.

(ii) Calculate the reaction Gibbs energy, Delta G_r, when at some time during the course of the reaction, the reaction quotient, Q, is 0.01.

(iii) What is the difference in chemical potential between the two species when Q = 0.01?

2Medium15 marks

Predict the products and give the mechanisms involved in the following chemical transformations :

3Medium10 marks

A bomb calorimeter has a measured heat capacity of 6.27 kJ/°C. The combustion of 1.84 g of magnesium (at. wt. = 24.3 g mol^-1) leads to a temperature change from 21.30 °C to 25.56 °C. The specific heat of water is 4.18 J/°C/g.

(i) Calculate the change in internal energy (Delta u) per mole of Mg for the reaction Mg(s) + 1/2 O2(g) -> MgO(s).

(ii) If the reaction were carried out open to the atmosphere at 25 °C, what would be the enthalpy change (Delta H) of the reaction per mole of Mg?

Chemistry UPSC PYQ 2015

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