Consider the decomposition of liquid benzene, C 6 H 6 (l), to gaseous acetylene, C 2 H 2 (g): C 6 H 6 (l) → 3 C2H 2 (g) ΔH = +630 kJ (b) What is H for the formation of 1 mol of acetylene?

hey everyone in this example, we have the following reaction And we need to find the entropy of formation of 5.15 g of lead chloride. So we want to recognize whether our equation is balanced and based on our psyche aama tree and the coefficients. It's definitely a balanced equation. Our next step is to recognize that we are given the entropy of formation for reaction for our formation of lead chloride as negative 3 36 point okay, joules per mole and this is for one mole of our lead chloride. So we want to recognize that that comes from the coefficient one which is in front of our product lead chloride. So our next step is to first because we are given the amount in grams for lead chloride. We need to convert from grams to moles. So we want to start from 5.15 g of our lead chloride. And then we're going to go from grams to moles by recalling our molar mass for the compound. So when we find lead in group four a on our periodic tables, we see that it has a molar mass of 207.2 g per mole. And when we find chlorine in group seven a on the periodic table, We see that it has a molar mass of 35.4, 5 g per mole. Now recognize that in our formula, we have two moles of our Chlorine Atom. And so we're going to multiply this by two. So to get the total mass for the compound lead chloride, we're going to have these two masses added up together And we're going to have a total of 278.1 g per mole for our compound P BCL two. So we're going to plug that in. So we have to 78.1 g for one mole of our lead chloride. So this allows us to cancel out our units of grams leaving us with moles, which is what we want. And we're going to get a value equal to 0.01815 moles of our lead chloride. And actually I re I just need to rewrite this number. So it's actually 0.018 519 moles of our lead chloride. And so now we can calculate our anthem P A formation for our lead chloride For our 5.15 g of lead chloride. And we would get that that is equal to our entropy of formation for one mole, which is given as negative 3 36.0 Killer Jewels for one mole of lead chloride. And then we're multiplying this by our molds of our 5.15 g of our lead chloride which we found above. So we plugged that in as 0. moles of our lead chloride. So this allows us to cancel out most, leaving us with kayla jewels as our final unit, Which is definitely what we need for entropy of formation. And we get a value in our calculators equal to negative 6.22238. So we can round this to about 366 so that we have negative 6.22 kg joules as our final answer For the entropy of formation of our 5. g of our product, lead chloride. So I hope that everything we reviewed was clear. If you have any questions, please leave them down below and I will see everyone in the next practice video.

Ch.5 - Thermochemistry

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Brown 14th Edition

Ch.5 - Thermochemistry

Problem 48b

Chapter 5, Problem 48b

Consider the decomposition of liquid benzene, C₆H₆(l), to gaseous acetylene, C₂H₂(g): C₆H₆(l) → 3 C2H₂(g) ΔH = +630 kJ (b) What is H for the formation of 1 mol of acetylene?

Verified step by step guidance

Identify the given reaction and its enthalpy change: The decomposition of 1 mole of liquid benzene (C6H6(l)) into 3 moles of gaseous acetylene (C2H2(g)) has an enthalpy change (ΔH) of +630 kJ.

Understand the relationship between the moles of benzene and acetylene: From the reaction, 1 mole of benzene produces 3 moles of acetylene.

Calculate the enthalpy change per mole of acetylene produced: Since the total enthalpy change for the reaction is +630 kJ for 3 moles of acetylene, divide this value by 3 to find the enthalpy change per mole of acetylene.

Express the enthalpy change for the formation of 1 mole of acetylene: The result from the previous step gives the enthalpy change (ΔH) for the formation of 1 mole of acetylene from benzene.

Note the sign of ΔH: Since the overall reaction is endothermic (+630 kJ), the enthalpy change per mole of acetylene will also be positive, indicating that energy is absorbed in the formation of acetylene from benzene.

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Key Concepts

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

Thermochemistry

Thermochemistry is the study of the heat energy associated with chemical reactions and physical transformations. It involves understanding how energy is absorbed or released during these processes, which is crucial for calculating enthalpy changes (ΔH). In the given reaction, the positive ΔH indicates that the decomposition of benzene is endothermic, meaning it requires energy input.

Enthalpy of Formation

The enthalpy of formation (ΔH_f) is the change in enthalpy when one mole of a compound is formed from its elements in their standard states. This concept is essential for determining the energy changes associated with the formation of products from reactants. In this case, calculating the enthalpy for the formation of acetylene involves using the enthalpy change of the decomposition reaction and stoichiometric relationships.

Stoichiometry

Stoichiometry is the quantitative relationship between reactants and products in a chemical reaction. It allows chemists to calculate the amounts of substances consumed and produced in a reaction based on balanced chemical equations. For the decomposition of benzene to acetylene, stoichiometry helps determine how the enthalpy change relates to the formation of one mole of acetylene from the given reaction.