Calculate the standard heat of formation of the compound ICl(g) at 25^∘ C, and show your work. (

Calculate the standard heat of formation of the compound...

Key Concepts

Standard Heat of Formation

The standard heat of formation of a compound is the change in enthalpy when one mole of the compound is formed from its elements in their most stable forms at 25°C and 1 atm pressure. This value serves as a reference for calculating enthalpy changes in chemical reactions and is crucial in thermochemical calculations.

Hess's Law

Hess's Law states that the total enthalpy change of a chemical reaction is the same, regardless of the pathway taken. This principle allows one to calculate the enthalpy change for a reaction by summing the enthalpy changes of individual steps leading from reactants to products, making it especially useful when direct experimental data is not available.

Thermochemical Data Tables

Thermochemical data tables, such as those referenced in the problem, provide experimentally determined standard enthalpies of formation and other thermodynamic values. These tables serve as a reliable source for the numerical values required in performing enthalpy calculations and understanding reaction energetics.

Transcript

00:01 Okay, so this problem is asking us to calculate the standard heat of formation for icl in gas state at 25 celsius.

00:11 And i can think of that process as a two -step process.

00:14 First, i'm going to take iodine in solid state and turn it into iodine in gas state.

00:23 Why am i starting with a solid state? because the problem says that the reaction happens at 25 celsius.

00:30 So the natural state for iodine at 25 celsius is actually a solid.

00:36 Now, let's put a one -half coefficient for both the reactant and the product, so that i have a single iodine atom, which is what i'm going to use in the next reaction.

00:49 Now, the second step is to take that gas that i just formed, the iodine gas, and combine it with chlorine gas.

00:57 So i'm going to take the one -half iodine two gas plus one -half of chlorine two gas, combine them to form the compound that i'm looking for, which is the icl gas.

01:14 Okay? and that's why i took the one -half, because at the end we're looking for a single iodine and a single chlorine atom.

01:21 So putting those one -half coefficients allows for that reaction to be balanced.

01:26 So now all i have to do is calculate the delta h of each one of these two reactions, sum them up, add them up, and then we're going to get the overall formation heat for that reaction.

01:38 So how do we get the delta h for the first reaction? well, for that we can actually use appendix 4, which is what the problem suggests.

01:49 So if we look at appendix 4, the thermodynamic values, we can look at the heats of formation.

01:55 So we're going to find that the heat of formation at standard conditions, which is the temperature that we're looking for, for i2 solid is going to be zero, because that is the most stable state.

02:11 And the heat of formation for i2 gas is 62 kj per mol.

02:21 So we're going to use that in our first reaction.

02:25 So we know that for the first reaction, delta h of the reaction is going to be the heats of formation of the products times the coefficients.

02:36 The coefficients are one -half, so i'm going to have one -half times 62 minus the heat of formation for the reactants, which is actually zero...

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