The following reaction is used in the industrial synthesis of polyvinyl chloride (PVC) polymer: Cl 2 (g) + H 2 C=CH 2 (g) → ClCH 2 CH 2 Cl( l ) ∆H = –52 kcal/mol (–218 kJ/mol) a. Is ∆ S positive or negative for this process?

Welcome back, everyone is delta S or entropy change positive or negative for the synthesis of liquid ammonia. NH three. Let's recall our facts about entropy. S recall that s represents our symbol for entropy and it describes the degree of chaos and disorder of a system. So if we have a positive change in entropy or positive delta us, this means we have an increase in entropy. Whereas if we have a negative delta S value, we have a decrease in entropy or disorder of our system. Recall that our gas face has the highest amount of entropy versus our liquid face, which has a lower amount of entropy. And our liquid phase has a greater amount of entropy than our solid phase, which has the lowest amount of entropy. So let's see how our phases change from our react inside to our product side. In our given reaction. In our given reaction, we have three moles of hydrogen gas reacting with two moles of nitrogen gas to produce two moles of liquid ammonia were given delta H which is our Anthill be change equal to negative 38.4 kilocalories per mole also equivalent to negative 161 kg joules per mole on our react inside, we can count a total of four moles of gas. Versus on the product side, we just have to molds of liquid. Our four moles of gas from our react inside comes from our three moles of our di atomic hydrogen gas plus our one mole of our di atomic nitrogen gas. And that gives us our four moles of gas on the react inside. As we stated, our gaseous state has higher entropy than our liquid state. And so this means that we went from higher entropy on the reactant side to lower entropy on the product side with just our liquid state being present. And because we went from higher entropy to lower entropy, we would say that therefore, our entropy change is going to be negative. And so delta S is going to be negative as our final answer. And this is going to correspond to choice b in the multiple choice which states that entropy is negative for the synthesis of liquid ammonia. So I hope this made sense and let us know if you have any questions.

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7. Energy, Rate and Equilibrium

Entropy (Simplified)

GOB Chemistry

7. Energy, Rate and Equilibrium

Entropy (Simplified)

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2:50 minutes

Problem 40a

Textbook Question

The following reaction is used in the industrial synthesis of polyvinyl chloride (PVC) polymer:
Cl₂(g) + H₂C=CH₂(g) → ClCH₂CH₂Cl(l) ∆H = –52 kcal/mol (–218 kJ/mol)
a. Is ∆S positive or negative for this process?

Verified step by step guidance

Step 1: Begin by analyzing the reaction. The reactants are chlorine gas (Cl₂) and ethene (H₂C=CH₂), both in the gaseous state, while the product is 1,2-dichloroethane (ClCH₂CH₂Cl), which is in the liquid state. This phase change is important for determining the entropy change (∆S).

Step 2: Recall that entropy (S) is a measure of disorder or randomness in a system. Gases have higher entropy compared to liquids because gas particles are more disordered and have more freedom of movement.

Step 3: Observe that the reaction starts with two gaseous molecules (Cl₂ and H₂C=CH₂) and produces one liquid molecule (ClCH₂CH₂Cl). This indicates a decrease in the number of particles and a transition from a gaseous state to a liquid state, both of which typically result in a decrease in entropy.

Step 4: Consider the overall system. The reduction in the number of particles and the phase change from gas to liquid suggest that the system becomes more ordered, leading to a negative ∆S value.

Step 5: Conclude that ∆S for this process is negative because the reaction results in fewer particles and a transition to a more ordered liquid state, reducing the overall entropy of the system.

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Key Concepts

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

Entropy (∆S)

Entropy, denoted as ∆S, is a measure of the disorder or randomness in a system. In chemical reactions, a positive ∆S indicates an increase in disorder, while a negative ∆S suggests a decrease in disorder. Understanding how the arrangement of molecules changes during a reaction is crucial for predicting the sign of ∆S.

Reaction Mechanism

The reaction mechanism describes the step-by-step process by which reactants are converted into products. In the given reaction, the addition of chlorine to ethylene involves breaking and forming bonds, which can affect the molecular arrangement and thus the entropy. Analyzing the mechanism helps in determining how the reaction influences the system's disorder.

Thermodynamics of Reactions

Thermodynamics provides the framework for understanding energy changes in chemical reactions, including enthalpy (∆H) and entropy (∆S). The relationship between these two properties is described by the Gibbs free energy equation (∆G = ∆H - T∆S). For the given reaction, knowing the enthalpy change helps infer the likely change in entropy, as exothermic reactions often lead to a decrease in disorder.

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