Calculate ΔH rxn for the reaction: Fe 2 O 3 (s) + 3 CO(g) → 2 Fe(s) + 3 CO 2 (g) Use the following reactions and given ΔH's: 2 Fe(s) + 3/2 O 2 (g) → Fe 2 O 3 (s) ΔH = –824.2 kJ CO(g) + 1/2 O 2 (g) → CO 2 (g) ΔH = –282.7 kJ

Hello, everyone today with the following problem, calculate the change in entropy for the following reaction, use the following reactions and given entropy changes. So we first have to look at our reactions and compare them with the overall reaction. So with reaction one, we see here that we have our iron, our ferrous oxide on the product side. So our over our in our overall reaction, we have it on the reactant side. So we need to essentially reverse the sign of entropy such that it is positive 8 24.2 kilo joules. Looking at our second reaction, we look at the reactant side and the overall reaction has three moles of carbon dioxide or overall reaction. Well, our reaction two has only one more. And so we need to multiply the second reaction. And the envoy by three recall that we have to multiply everything by the same variable. So that would essentially give us a change in entropy of negative 8 48.1 kilojoules. And so we also have to recall hess's law that states that the entropy change of the net reaction is the sum of the entropy of the steps. So if you want to find the ultimate or the final entropy of the reaction, we take our reaction one which is 824 0.2 killer jules. And we add that to the second reactions entropy which is negative 8 48.1 kilojoules. And in doing so, we arrive in an answer of negative 23.9 kilojoules or answer twice a overall, I hope it's helped. And until next time.

Ch.7 - Thermochemistry

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Tro 5th Edition

Ch.7 - Thermochemistry

Problem 79

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Chapter 7, Problem 79

Calculate ΔH_rxn for the reaction:
Fe₂O₃(s) + 3 CO(g) → 2 Fe(s) + 3 CO₂(g)
Use the following reactions and given ΔH's:
2 Fe(s) + 3/2 O₂(g) → Fe₂O₃(s) ΔH = –824.2 kJ
CO(g) + 1/2 O₂(g) → CO₂(g) ΔH = –282.7 kJ

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Identify the given reactions and their respective enthalpy changes (ΔH). For the first reaction: 2 Fe(s) + 3/2 O2(g) → Fe2O3(s) with ΔH = -824.2 kJ. For the second reaction: CO(g) + 1/2 O2(g) → CO2(g) with ΔH = -282.7 kJ.

Write the target reaction for which you need to calculate ΔHrxn: Fe2O3(s) + 3 CO(g) → 2 Fe(s) + 3 CO2(g).

Reverse the first given reaction to match the products and reactants of the target reaction. The reversed reaction is: Fe2O3(s) → 2 Fe(s) + 3/2 O2(g). Reversing the reaction changes the sign of ΔH, so ΔH becomes +824.2 kJ.

Multiply the second given reaction by 3 to balance the number of CO and CO2 in the target reaction: 3[CO(g) + 1/2 O2(g) → CO2(g)]. This also multiplies the ΔH by 3, giving 3(-282.7 kJ) = -848.1 kJ.

Add the modified reactions from steps 3 and 4 to get the target reaction. Add their ΔH values to find the ΔHrxn for the target reaction: ΔHrxn = +824.2 kJ + (-848.1 kJ).

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Hess's Law

Hess's Law states that the total enthalpy change for a chemical reaction is the sum of the enthalpy changes for the individual steps of the reaction, regardless of the pathway taken. This principle allows us to calculate the enthalpy change (ΔHrxn) for a reaction by using known ΔH values from related reactions, making it essential for solving problems involving reaction enthalpies.

Standard Enthalpy of Formation

The standard enthalpy of formation (ΔHf°) is the change in enthalpy when one mole of a compound is formed from its elements in their standard states. This concept is crucial for calculating ΔHrxn, as it provides a reference point for the energy changes associated with the formation of reactants and products in a chemical reaction.

Stoichiometry in Thermochemistry

Stoichiometry in thermochemistry involves using the coefficients from a balanced chemical equation to relate the amounts of reactants and products to their respective enthalpy changes. Understanding stoichiometry is vital for accurately calculating ΔHrxn, as it ensures that the enthalpy changes are applied in proportion to the quantities of substances involved in the reaction.

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