Without referring to tables, predict which of the following has the higher enthalpy in each case: (c) 1 mol I 2 (g) and 1 mol H 2 (g) at 25 °C or 2 mol HI(g) at 25 °C (d) 1 mol H 2 (g) at 100 °C or 1 mol H 2 (g) at 300 °C.

Hello. Everyone in this video, we're trying to see if this five g of 02 in its gaseous phase versus the five g of the 02 and its liquid phase has which one has a greater anthem P. At the same exact temperature. Well think of it as a different way. So we first know that liquid can turn to gas. But what is this process called more was this process in general? This is what we call evaporation even operation. So in order for the oxygen liquid to turn into oxygen gas, it's going to go through this process right here and this requires heat. If you think about it, let's say we have water instead of the 02. If we have liquid water and we want liquid paper, then we need to add heat boiling the water until it becomes gas. You know, in the cartoon character in the cartoon animations, we have a pot of water maybe or a cup of water and it has like maybe the steam coming out. This steam is going to be all of its gasses states of the water. So that's what I think about. And so because we require heat, We need higher entropy. So therefore we can say that the five g of the gas has higher or greater entropy. And this is going to be our final answer for this question. Thank you so much for watching

Ch.5 - Thermochemistry

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Brown 14th Edition

Ch.5 - Thermochemistry

Problem 42c,d

Chapter 5, Problem 42c,d

Without referring to tables, predict which of the following has the higher enthalpy in each case: (c) 1 mol I₂(g) and 1 mol H₂(g) at 25 °C or 2 mol HI(g) at 25 °C (d) 1 mol H₂(g) at 100 °C or 1 mol H₂(g) at 300 °C.

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Identify the chemical reaction involved: I_2(g) + H_2(g) -> 2 HI(g).

Understand that enthalpy is a measure of the total energy of a thermodynamic system, often associated with the heat content.

Recognize that the formation of bonds releases energy (exothermic), while breaking bonds requires energy (endothermic).

Consider the bond energies: breaking the I-I and H-H bonds requires energy, while forming two H-I bonds releases energy.

Predict that the enthalpy of the products (2 mol HI) is lower than the enthalpy of the reactants (1 mol I_2 and 1 mol H_2) because the formation of HI releases more energy than is required to break the I_2 and H_2 bonds.

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Key Concepts

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

Enthalpy of Formation

Enthalpy of formation refers to the change in enthalpy when one mole of a compound is formed from its elements in their standard states. It is a crucial concept in thermodynamics, as it helps predict the stability and energy content of compounds. For example, the formation of hydrogen iodide (HI) from hydrogen (H2) and iodine (I2) involves specific enthalpy changes that can be compared to the enthalpy of the reactants.

Bond Energies

Bond energies represent the amount of energy required to break a bond between two atoms in a molecule. The strength of these bonds directly influences the enthalpy of a substance; stronger bonds typically correlate with lower enthalpy. In the case of HI, the bond energy between H and I will affect the overall enthalpy when comparing it to the elemental gases I2 and H2.

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 taken to achieve the reaction. This principle allows for the calculation of enthalpy changes by summing the enthalpy changes of individual steps. In this question, Hess's Law can be applied to compare the enthalpy of the reactants (I2 and H2) with the product (HI) to determine which has a higher enthalpy.

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Hess's Law

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Textbook Question

Atomic hydrogen (H) is used in welding (AHW). The atoms recombine to hydrogen molecules with a large release of heat according to the following reaction: 2 H(g) → H₂(g) (b) Which has the higher enthalpy under these conditions, 2 H(g) or H₂(g)?

Textbook Question

Without referring to tables, predict which of the following has the higher enthalpy in each case: (a) 1 mol I₂(s) or 1 mol I₂(g) at the same temperature

Textbook Question

Without referring to tables, predict which of the following has the higher enthalpy in each case: (b) 2 mol of iodine atoms or 1 mol of I₂

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Textbook Question

Consider the following reaction: 2 CH₃OH(g) → 2 CH₄(g) + O₂(g) ΔH = +252.8 kJ (b) Calculate the amount of heat transferred when 24.0 g of CH₃OH(g) is decomposed by this reaction at constant pressure.

Textbook Question

Consider the following reaction: 2 CH₃OH(g) → 2 CH₄(g) + O₂(g) ΔH = +252.8 kJ (c) For a given sample of CH₃OH, the enthalpy change during the reaction is 82.1 kJ. How many grams of methane gas are produced?

Without referring to tables, predict which of the following has the higher enthalpy in each case: (c) 1 mol I2(g) and 1 mol H2(g) at 25 °C or 2 mol HI(g) at 25 °C (d) 1 mol H2(g) at 100 °C or 1 mol H2(g) at 300 °C.

Verified video answer for a similar problem:

Key Concepts

Enthalpy of Formation

Bond Energies

Hess's Law

Without referring to tables, predict which of the following has the higher enthalpy in each case: (c) 1 mol I₂(g) and 1 mol H₂(g) at 25 °C or 2 mol HI(g) at 25 °C (d) 1 mol H₂(g) at 100 °C or 1 mol H₂(g) at 300 °C.