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Ch.15 - Chemical Equilibrium
Chapter 15, Problem 66a

Methanol (CH3OH) can be made by the reaction of CO with H2: CO(𝑔) + 2 H2(𝑔) β‡Œ CH3OH(𝑔) (a) Use thermochemical data in Appendix C to calculate Ξ”HΒ° for this reaction.

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Key Concepts

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

Thermochemical Data

Thermochemical data includes information about the enthalpy changes associated with chemical reactions. This data is often found in tables and can provide standard enthalpy of formation values (Ξ”HΒ°f) for various substances. By using these values, one can calculate the overall enthalpy change (Ξ”HΒ°) for a reaction by applying Hess's law, which states that the total enthalpy change is the sum of the enthalpy changes for individual steps.
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Hess's Law

Hess's Law states that the total enthalpy change for a chemical reaction is the same, regardless of the number of steps or the pathway taken. This principle allows chemists to calculate the enthalpy change of a reaction by summing the enthalpy changes of individual reactions that lead to the same products. It is particularly useful when direct measurement of Ξ”HΒ° is difficult or impossible.
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Standard Enthalpy of Formation (Ξ”HΒ°f)

The standard enthalpy of formation (Ξ”HΒ°f) is defined as the change in enthalpy when one mole of a compound is formed from its elements in their standard states. This value is crucial for calculating the enthalpy change of a reaction using the formula Ξ”HΒ° = ΣΔHΒ°f(products) - ΣΔHΒ°f(reactants). Understanding how to use Ξ”HΒ°f values allows for the determination of the energy changes involved in chemical reactions.
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Related Practice
Textbook Question

Consider the reaction 4 NH3(𝑔) + 5 O2(𝑔) β‡Œ 4 NO(𝑔) + 6 H2O(𝑔), Δ𝐻 = βˆ’904.4 kJ Does each of the following increase, decrease, or leave unchanged the yield of NO at equilibrium? (e) add a catalyst

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Textbook Question

Consider the reaction 4 NH3(𝑔) + 5 O2(𝑔) β‡Œ 4 NO(𝑔) + 6 H2O(𝑔), Δ𝐻 = βˆ’904.4 kJ Does each of the following increase, decrease, or leave unchanged the yield of NO at equilibrium? (f) increase temperature.

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Textbook Question

Consider the following equilibrium between oxides of nitrogen 3 NO(g) β‡Œ NO2(g) + N2O(g) (a) At constant temperature, would a change in the volume of the container affect the fraction of products in the equilibrium mixture?

Textbook Question

Methanol (CH3OH) can be made by the reaction of CO with H2: CO(𝑔) + 2 H2(𝑔) β‡Œ CH3OH(𝑔) (b) To maximize the equilibrium yield of methanol, would you use a high or low temperature?

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Textbook Question

Methanol (CH3OH) can be made by the reaction of CO with H2: CO(𝑔) + 2 H2(𝑔) β‡Œ CH3OH(𝑔) (c) To maximize the equilibrium yield of methanol, would you use a high or low pressure?

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Textbook Question

Ozone, O3, decomposes to molecular oxygen in the stratosphere according to the reaction 2 O3(𝑔) ⟢ 3 O2(𝑔). Would increasing the pressure by decreasing the size of the reaction vessel favor the formation of ozone or of oxygen?