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Test: Enthalpy Change, ∆rH of a Reaction - Chemistry MCQ


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10 Questions MCQ Test - Test: Enthalpy Change, ∆rH of a Reaction

Test: Enthalpy Change, ∆rH of a Reaction for Chemistry 2024 is part of Chemistry preparation. The Test: Enthalpy Change, ∆rH of a Reaction questions and answers have been prepared according to the Chemistry exam syllabus.The Test: Enthalpy Change, ∆rH of a Reaction MCQs are made for Chemistry 2024 Exam. Find important definitions, questions, notes, meanings, examples, exercises, MCQs and online tests for Test: Enthalpy Change, ∆rH of a Reaction below.
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Test: Enthalpy Change, ∆rH of a Reaction - Question 1

The standard state of a substance is considered when the temperature is 298 k and the pressure is ____________

Detailed Solution for Test: Enthalpy Change, ∆rH of a Reaction - Question 1

All the standard states of a substance are considered when the temperature is 298 Kelvin and the pressure is 1 bar. 1 bar = 0.987 atmospheric pressure = 10000 Pascal = 750.0617 mm of Mercury.

Test: Enthalpy Change, ∆rH of a Reaction - Question 2

Consider that, a ball is immersed in water at room temperature and then taken out having 18 grams of water on it, how much amount of energy is required to dry that water at room temperature?

Detailed Solution for Test: Enthalpy Change, ∆rH of a Reaction - Question 2

Heat required to eliminate water : n x ΔvapH = (1 mol) × (44.01 kJ mol–1) = 44.01 kJ mol-1. Δvapor = ΔvapH – ΔnRT = 44.01 kJ mol-1 – 1×8.314 J/K-mol x 298 k x 10-3 = 41.53 KJ/mol. So the amount of energy needed is 41.53 KJ/mol.

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Test: Enthalpy Change, ∆rH of a Reaction - Question 3

What is a change in energy if 18 grams of water is heated from room temperature to 20 degrees above it?

Detailed Solution for Test: Enthalpy Change, ∆rH of a Reaction - Question 3

We know that Q = msΔT, where Q is the energy,m is the mass of water, s is the specific heat of water and T is the temperature. So the change in energy required here = 18 g x 4.184 J/g-K x 20K = 1.506KJ.

Test: Enthalpy Change, ∆rH of a Reaction - Question 4

Consider the equation 2 H2 + O2 → 2 H2O, what does the 2 in the coefficient of H2O molecule represent?

Detailed Solution for Test: Enthalpy Change, ∆rH of a Reaction - Question 4

In a balanced thermochemical equation, the coefficients always refer to the number of the moles (but never molecules) of reactants and products involved in a reaction so 2 in the coefficient of H2O refers to the number of the moles of water.

Test: Enthalpy Change, ∆rH of a Reaction - Question 5

Which of the following is not an application of Hess’s law?

Detailed Solution for Test: Enthalpy Change, ∆rH of a Reaction - Question 5

The following are the applications of Hess’s law; determination of heat of formation, determination of heat of transition and determination of heat of hydration, also to calculate bond energies.

Test: Enthalpy Change, ∆rH of a Reaction - Question 6

All the enthalpies of fusion are positive.

Detailed Solution for Test: Enthalpy Change, ∆rH of a Reaction - Question 6

Fusion is a process of conversion of liquid to solid the enthalpy is energy that is required for a process. As the melting of a solid is endothermic, the enthalpies of fusion are positive so the above statement is true.

Test: Enthalpy Change, ∆rH of a Reaction - Question 7

Calculate the internal energy change when 2 moles of water at 0 degrees converts into ice at 0-degree centigrade?

Detailed Solution for Test: Enthalpy Change, ∆rH of a Reaction - Question 7

Energy change when 1 mol of water at 0-degree centigrade changes into ice at 0 degrees in centigrade is 6 kJ/mol, So the internal energy change when 2 moles of water at 0 degrees converts into ice at 0 degrees is 12 kJ/mole.

Test: Enthalpy Change, ∆rH of a Reaction - Question 8

When a chemical reaction is reversed the value of enthalpy is reversed in sign.

Detailed Solution for Test: Enthalpy Change, ∆rH of a Reaction - Question 8

For example, the formation of ammonia has an enthalpy of -91.8 KJ per mole and the decomposition of ammonia has an enthalpy of + 91.8 KJ per Mol. So the above statement that when a chemical reaction is reversed the value of enthalpy is reversed in the sign is true.

Test: Enthalpy Change, ∆rH of a Reaction - Question 9

What is the unit of standard enthalpy of fusion or molar enthalpy of fusion?

Detailed Solution for Test: Enthalpy Change, ∆rH of a Reaction - Question 9

The enthalpy change that occurs during melting of one mole of a solid substance in the standard state is called standard enthalpy of fusion or molar enthalpy of fusion, it is represented by the symbol ΔfusH, the units of this are KJ per Mol.

Test: Enthalpy Change, ∆rH of a Reaction - Question 10

ΔHr = Σ ΔHf[products] – Σ ΔHf[reactants].

Detailed Solution for Test: Enthalpy Change, ∆rH of a Reaction - Question 10

The equation ΔHr = Σ ΔHf[products] – Σ ΔHf[reactants] says that the enthalpy of a reaction is the difference between the enthalpy of products and enthalpy of reactants. The above statement regarding enthalpy is true.

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