List of top Chemistry Questions

Explain the terms Inductive and Electromeric effects. Which electron displacement effect explains the following correct orders of acidity of the carboxylic acids? 
\((a) Cl_3CCOOH>Cl_2CHCOOH>ClCH_2COOH \)
\((b) CH_3CH_2COOH>(CH_3)_2CHCOOH>(CH_3)_3C.COOH.\)

In the estimation of sulphur by Carius method, 0.468 g of an organic sulphur compound afforded 0.668 g of barium sulphate. Find out the percentage of sulphur in the given compound.

Draw the resonance structures for the following compounds. Show the electron shift using curved-arrow notation. 
(a) \(C_6H_5OH \)
(b) \(C_6H_5NO_2\) 
(c) \( CH_3CH=CHCHO\) 
(d) \(C_6H_5–CHO \)
(e) \(C_6H_5–C+H_2\)
(f) \(CH_3CH=CH C+H_2\)

The best and latest technique for isolation, purification and separation of organic compounds is

The reaction of cyanamide, \(NH_2CN(s)\), with dioxygen was carried out in a bomb calorimeter, and \(∆U\) was found to be \(–742.7\ kJ\ mol^{–1}\) at \(298\ K\). Calculate enthalpy change for the reaction at \(298\ K\).
\(NH_2CN(g)+\frac 32O_2(g)→N_2(g)+CO_2(g)+H_2O(l)\)

In a process, 701 J of heat is absorbed by a system and 394 J of work is done by the system. What is the change in internal energy for the process?

Justify that the following reactions are redox reactions:

1. \(CuO(s) + H_2(g) \rightarrow Cu(s) + H_2O(g) \)
2. \(Fe_2O_3(s) + 3CO(g) \rightarrow 2Fe(s) + 3CO_2(g) \)
3. \(4BCl_3(g) + 3LiAlH_4(s) \rightarrow 2B_2H_6(g) + 3LiCl(s) + 3 AlCl_3 (s) \)
4. \(2K(s) + F_2(g) \rightarrow 2K+F^- (s) \)
5. \(4 NH_3(g) + 5 O_2(g) \rightarrow 4NO(g) + 6H_2O(g)\)

Enthalpy of combustion of carbon to CO₂ is –393.5 kJ mol^–1. Calculate the heat released upon formation of 35.2 g of CO₂ from carbon and dioxygen gas.

The reaction CH₃CH₂I + KOH(aq) \(\rightarrow\) CH₃CH₂OH + KI is classified as 

Enthalpies of formation of CO(g), CO₂(g), N₂O(g) and N₂O₄(g) are –110, – 393, 81 and 9.7 kJ mol^-1 respectively. Find the value of ∆_rH for the reaction.
\(N_2O_4(g) + 3CO(g) → N_2O(g) + 3CO_2(g)\)

In the organic compound \(CH_2 = CH-CH_2-CH_2-C≡CH\), the pair of hydridised orbitals involved in the formation of \(C_2 – C_3\) bond is

Given, \(N_2(g) + 3H_2(g)→2NH_3(g)\); \(∆_rH^Θ=-92.4\ kJ mol^{–1}\)
What is the standard enthalpy of formation of \(NH_3\) gas?

Calculate the standard enthalpy of formation of \(CH_3OH(l)\) from the following data.
\(CH_3OH (l) +\frac 32 O_2(g)→CO_2(g)+2H_2O (l)\) ;  \( ∆_rH^Θ= –726 \ kJ mol^{–1}\),
\(C(graphite)+O_2(g)→CO_2(g)\);  \(∆_cH^Θ = –393 \ kJ mol^{–1}\),
\(H_2(g)+\frac 12 O_2(g)→H_2O (l)\);  \(∆_f H^Θ= –286 kJ mol^{–1}\)

Calculate the enthalpy change for the process
\(CCl_4(g) → C(g) + 4Cl(g)\)
and calculate bond enthalpy of \(C-Cl\) in \(CCl_4(g)\).
\(∆_{vap}H^Θ(CCl_4) = 30.5\ kJ mol^{-1}\).
\(∆_fH^Θ(CCl_4)= –135.5\ kJ mol^{-1}\).
\(∆_aH^Θ (C)= 715.0\ kJ mol^{-1}\),    where \(∆_aH^Θ\) is enthalpy of atomisation.
\(∆_aH^Θ (Cl_2) = 242\ kJ mol^{-1}\).

For an isolated system, ∆U=0, what will be ∆S ?

For the reaction at \(298\ K\),
\(2A+B→C\)
\(∆H = 400\ kJ mol^{-1}\) and \(∆S = 0.2\ kJ K^{-1} mol^{-1}\)
At what temperature will the reaction become spontaneous considering \(∆H\) and \(∆S\) to be constant over the temperature range.

For the reaction, \(2Cl(g)→Cl_2(g)\), what are the signs of \(∆H\) and \(∆S\) ?

For the reaction
\(2A(g)+B(g)→2D(g)\)
\(∆U^Θ= -10.5\ kJ\) and \(∆S^Θ= -44.1\ JK^{-1}\).
Calculate \(∆G^Θ\) for the reaction, and predict whether the reaction may occur spontaneously.

The equilibrium constant for a reaction is \(10\). What will be the value of \(∆G^Θ\)?
\(R= 8.314\ JK^{-1} mol^{-1}, T=300\ K\)

The enthalpy of combustion of methane, graphite and dihydrogen at 298 K are, -890.3 kJ mol^-1, -393.5 kJ mol^-1, and -285.8 kJ mol^-1 respectively. Enthalpy of formation of CH₄(g) will be

Comment on the thermodynamic stability of \(NO(g)\), given
\(\frac 12N_2(g) +\frac 12O_2(g)→NO(g); \ \ \ \ ∆_rH^Θ= 90\ kJ mol^{-1}\)
\(NO(g) +\frac 12 O_2(g)→NO_2(g);\ \ \  ∆_rH^Θ= –74\ kJ mol^{-1}\)

Calculate the entropy change in surroundings when \(1.00\ mol\) of \(H_2O(l)\) is formed under standard conditions. \(∆_fH^Θ= –286\ kJ mol^{-1}\).

Why is Wurtz reaction not preferred for the preparation of alkanes containing odd number of carbon atoms? Illustrate your answer by taking one example

Discuss the chemistry of Lassaigne’s test.

Determine the molecular formula of an oxide of iron, in which the mass per cent of iron and oxygen are 69.9 and 30.1, respectively.