Join WhatsApp Icon JEE WhatsApp Group
Question 52

Two reactions are given below:
$$2Fe_{(s)} + \frac{3}{2}O_{2(g)} \rightarrow Fe_2O_{3(s)}$$, $$\Delta H° = -822$$ kJ/mol
$$C_{(s)} + \frac{1}{2}O_{2(g)} \rightarrow CO_{(g)}$$, $$\Delta H° = -110$$ kJ/mol
Then enthalpy change for following reaction:
$$3C_{(s)} + Fe_2O_{3(s)} \rightarrow 2Fe_{(s)} + 3CO_{(g)}$$


Correct Answer: 492

We need to find the enthalpy change for the reaction:

$$ 3C_{(s)} + Fe_2O_{3(s)} \rightarrow 2Fe_{(s)} + 3CO_{(g)} $$

We are given two reactions:

The first is $$2Fe_{(s)} + \frac{3}{2}O_{2(g)} \rightarrow Fe_2O_{3(s)}$$, $$\Delta H_1° = -822$$ kJ/mol.

The second is $$C_{(s)} + \frac{1}{2}O_{2(g)} \rightarrow CO_{(g)}$$, $$\Delta H_2° = -110$$ kJ/mol.

Hess's Law states that the enthalpy change of an overall reaction is the sum of the enthalpy changes of the individual steps, regardless of the pathway taken, so we manipulate the given reactions to arrive at the target reaction.

Since the target reaction has $$Fe_2O_{3}$$ as a reactant and $$Fe$$ as a product, we reverse the first reaction, which changes the sign of $$\Delta H$$:

$$ Fe_2O_{3(s)} \rightarrow 2Fe_{(s)} + \frac{3}{2}O_{2(g)}, \quad \Delta H = +822 \text{ kJ/mol} $$

The target reaction requires 3 moles of C and produces 3 moles of CO, so we multiply the second reaction by 3; this also multiplies its enthalpy change by 3:

$$ 3C_{(s)} + \frac{3}{2}O_{2(g)} \rightarrow 3CO_{(g)}, \quad \Delta H = 3 \times (-110) = -330 \text{ kJ/mol} $$

Adding the reversed iron oxide reaction and the scaled carbon reaction gives:

$$ Fe_2O_{3(s)} + 3C_{(s)} + \frac{3}{2}O_{2(g)} \rightarrow 2Fe_{(s)} + \frac{3}{2}O_{2(g)} + 3CO_{(g)} $$

The $$\frac{3}{2}O_{2(g)}$$ appears on both sides and cancels out, yielding:

$$ 3C_{(s)} + Fe_2O_{3(s)} \rightarrow 2Fe_{(s)} + 3CO_{(g)} $$

This matches our target reaction.

$$ \Delta H_{total} = (+822) + (-330) = 822 - 330 = 492 \text{ kJ/mol} $$

The enthalpy change for the given reaction is $$\boxed{492}$$ kJ/mol.

Get AI Help

Video Solution

video

Create a FREE account and get:

  • Free JEE Mains Previous Papers PDF
  • Take JEE Mains paper tests

JEE Quant Questions | JEE Quantitative Ability

JEE DILR Questions | LRDI Questions For JEE

JEE Verbal Ability Questions | VARC Questions For JEE

Free JEE Topicwise Questions

JEE Rotational MotionJEE Units & MeasurementsJEE Atomic StructureJEE GravitationJEE Periodic Table & PeriodicityJEE StatisticsJEE Inverse Trigonometric FunctionsJEE Magnetism & Magnetic MaterialsJEE Sequences & SeriesJEE MatricesJEE Alternating CurrentsJEE Carboxylic AcidsJEE Permutations & CombinationsJEE Work, Energy & PowerJEE Electromagnetic InductionJEE Electronic DevicesJEE d and f-Block ElementsJEE Chemical KineticsJEE Heat TransferJEE Three Dimensional GeometryJEE Magnetic Effects of CurrentJEE Hydrocarbons - AromaticJEE Electromagnetic WavesJEE Aldehydes & KetonesJEE Hydrocarbons - AlkanesJEE Applications of DerivativesJEE EquilibriumJEE Indefinite IntegrationJEE Chemical ThermodynamicsJEE ElectrochemistryJEE ProbabilityJEE BiomoleculesJEE Continuity & DifferentiabilityJEE Kinetic Theory of GasesJEE Vector AlgebraJEE Hydrocarbons - AlkynesJEE Differential EquationsJEE Current & ResistanceJEE Straight LinesJEE WavesJEE Redox ReactionsJEE Hydrocarbons - AlkenesJEE DeterminantsJEE SolutionsJEE Ray OpticsJEE Dual Nature of Matter & RadiationJEE Chemical Bonding & Molecular StructureJEE Complex NumbersJEE Sets, Relations & FunctionsJEE Electric Charges & FieldsJEE Laws of MotionJEE Fluid MechanicsJEE Basic Concepts in ChemistryJEE Trigonometric FunctionsJEE LimitsJEE Laws of ThermodynamicsJEE Kinematics - 2D MotionJEE p-Block Elements (Groups 13-18)JEE Simple Harmonic MotionJEE Electric Potential & CapacitanceJEE Coordination CompoundsJEE JEE 2D GeometryJEE CirclesJEE Definite IntegrationJEE EMF & Circuit AnalysisJEE Surface TensionJEE Atoms & NucleiJEE Laboratory Experiments - XIJEE Number SystemJEE Basic Principles of Organic ChemistryJEE Wave OpticsJEE Quadratic EquationsJEE Alcohols, Phenols & EthersJEE Organic Compounds with HalogensJEE DifferentiationJEE Conic SectionsJEE Nitrogen-Containing CompoundsJEE ElasticityJEE Practical Organic ChemistryJEE Kinematics - 1D MotionJEE Purification & CharacterisationJEE Binomial Theorem
Ask AI