NEET Practice Questions (MCQs) with Answers & Solutions

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The first law of thermodynamics is only

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Explanation

First low of thermodynamics is also known as Law of conservation of mass and energy.

A mixture of two moles of carbon monoxide and one mole of oxygen, in a closed vessel is ignited to convert the carbon monoxide to carbon dioxide. If ΔH is the enthalpy change and ΔE is the change in internal energy, then [KCET 2005]

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Explanation

Formation of CO2 from CO is an exothermic reaction; heat is evolved from the system, i.e., energy is lowered. Thus, exothermic reactions occur spontaneously on account of decrease in enthapy of system. Thus, ΔE > ΔH.

The relation between ΔE and ΔH is [MP PET 1992; MP PMT 1996; MP PET/PMT 1998]

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Explanation

ΔH = ΔE + PΔV.

At constant T and P, which one of the following statements is correct for the reaction, CO(g)+12O2(g)CO2(g) [AIIMS 1982, 83; KCET 1988; BHU 1995; MP PET 1997, 99]

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Explanation

Δng=132=12, As Δng is negative, thus ΔH < ΔE.  

For the reaction of one mole of zinc dust with one mole of sulphuric acid in a bomb calorimeter, ΔU and w correspond to [AIIMS 2005]

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Explanation

Bomb calorimeter is commonly used to find the heat of combustion of organic substances which consists of a sealed combustion chamber, called a bomb. If a process is run in a sealed container then no expansion or compression is allowed, so w = 0 and ∆U = q.

∆U < 0, w = 0

If ΔH is the change in enthalpy and ΔE the change in internal energy accompanying a gaseous reaction [KCET 1989; CBSE PMT 1990]

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Explanation

If Δn = –ve than ΔH < ΔE.

Enthalpy for the reaction C + O2 → CO2 is [DPMT 1987, 91]

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Explanation

It is a combustion reaction, ΔH = –ve.

The work done in ergs for the reversible expansion of one mole of an ideal gas from a volume of 10 litres to 20 litres at 25°C is 

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Explanation

W=2.303  nRTlogV2V1

=2.303  ×1  ×8.314  ×107×298log2010

=298  ×107×8.314  ×2.303  log  2.

In a reversible isothermal process, the change in internal energy is

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Explanation

ΔE = 0 for reversible isothermal process.

The enthalpy of neutralization of which of the following acids and bases is nearly –13.6 Kcal [Roorkee 1999]

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Explanation

Heat of neutralisation of a strong acid and strong base is equal to –13.7 kcal.

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