Thermodynamics Test

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Thermodynamics Test - 21

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Question 1
1 / -0

Among the following enthalpies, which is always less than zero?

A
Δ_cH°

B
Δ_subH°

C
Δ_mixH°

D
Δ_fH°

Solution

The symbol represents enthalpy of combustion which is always exothermic. For exothermic rxn delta H is always -ve.
Question 2
1 / -0

Enthalpy change for a cyclic process is

A
negative

B
positive

C
not measurable

D
zero

Solution

Enthalpy is a state function; which means change in enthalpy depends only on final and initial state. So, the change in enthalpy for a cyclic process is zero.
Question 3
1 / -0

The solubility of fluorides is much less as compared to corresponding chlorides

A
because of low lattice enthalpy.

B
because of high lattice enthalpy.

C
because of low ionization energy.

D
because of high ionization energy.

Solution

Due to high lattice enthalpy of fluorides, it is difficult to break the lattice of fluoride compounds(due to the small size of fluorine, so the lattice is strong). SO the solubility of fluorides is less than chlorides.
Question 4
1 / -0

The enthalpy change when 1 mole of it dissolves in a specified amount of solvent is known as enthalpy of

A
solution

B
reaction

C
formation

D
none of the above

Solution

Enthalpy of solution (ΔHsoln) is the change in enthalpy that occurs when a specified amount of solute dissolves in a given quantity of solvent.
Question 5
1 / -0

The increasing order of enthalpy of vaporization of NH₃, PH₃, and AsH₃ is

A
NH₃, AsH₃, PH₃

B
NH₃, PH₃, AsH₃

C
AsH₃, PH₃, NH₃

D
PH₃, AsH₃, NH₃

Solution

The interparticle forces are strongest in NH₃ (Hydrogen bonding). In PH₃ and AsH₃ the inter-particle forces are dipole-dipole forces which are relatively stronger in AsH₃(due to higher mass of AsH₃). So the increasing order of vaporization is PH₃33 .
Question 6
1 / -0

The enthalpy of formation of NaCl can be calculated by using

A

B

C

D

Solution
Question 7
1 / -0

In Born-Haber cycle, the sum of the enthalpy changes around a cycle is

A
Negative integer

B
Zero

C
Constant

D
Positive integer

Solution

The Born-Haber cycle is based on Hess Law or Law of constant heat summation. It states that the standard enthalpy of reaction is the sum of algebraic sum of the standard enthalpies of reactions into which the overall reaction may be splitted. So the change in enthalpy around a cycle is zero.
Question 8
1 / -0

The enthalpies of fusion for all reactions are

A
Negative

B
Depends on the type of substance

C
Zero

D
Positive

Solution

The enthalpies of fusion for all reactions are always positive because melting of a solid is an endothermic process in which heat is supplied to the reaction Hence the sum of enthalpies of the product is greater than the sum of enthalpies of the reactant.
Question 9
1 / -0

In the reaction:

A
Enthalpy of combustion of hydrogen

B
Enthalpy of formation of water

C
Enthalpy of hydration of oxygen

D
Both enthalpy of combustion of hydrogen or enthalpy of formation of water

Solution

∆H_r is called both enthalpy of combustion of hydrogen as well as enthalpy of formation of water.For the enthalpy of combustion of hydrogen, the reason is that 1 mole of Hydrogen is burnt in its pure state. For the formation of water, the reason is that 1 mole of water is formed from its constituent elements.
Question 10
1 / -0

What happens to the ions, when an ionic compound dissolves in a solvent?

A
They leave their ordered position in the crystal lattice and gets hydrated.

B
They leave their ordered position in the crystal lattice and doesn’t hydrate.

C
They doesn’t leave their ordered position in the crystal lattice and gets hydrated.

D
None of the above.

Solution

When an ionic compound is dissolved in the solvent, the compound dissociate into ions and due to external medium i. e. solvent it leave its original position in crystal lattice n gets hydrated..
Eg. NaCl(aq) → Na+(aq) + Cl-(aq)