The rates of many atmospheric reactions are accelerated
by the ab...

Question

The rates of many atmospheric reactions are accelerated by the absorption of light by one of the reactants. For example, consider the reaction between methane and chlorine to produce methyl chloride and hydrogen chloride: Reaction 1: CH41g2 + Cl21g2 ¡ CH3Cl1g2 + HCl1g2 This reaction is very slow in the absence of light. However, Cl21g2 can absorb light to form Cl atoms: Reaction 2: Cl21g2 + hv ¡ 2 Cl1g2 Once the Cl atoms are generated, they can catalyze the reaction of CH4 and Cl2, according to the following proposed mechanism: Reaction 3: CH41g2 + Cl1g2 ¡ CH31g2 + HCl1g2 Reaction 4: CH31g2 + Cl21g2 ¡ CH3Cl1g2 + Cl1g2 The enthalpy changes and activation energies for these two reactions are tabulated as follows: Reaction H 1kJ ,mol 2 Ea 1kJ ,mol 2 3 +4 17 4 -109 4 (b) By using the data tabulated here, sketch a quantitative energy profile for the catalyzed reaction represented by reactions 3 and 4.

Accepted Answer

hi everyone for this problem. It reads photochemical reactions are catalyzed by the absorption of light by one of the reactant. For example, the formation and decomposition of ozone shown below the entropy changes. And activation energies for these two reactions are tabulated as follows. Draw the energy diagram and show the sequence for step two and three. All right. So we want to draw the energy diagram and show the sequence for a step two and three. So with an energy diagram, this shows the progress of a chemical reaction as a function of potential energy. And so when we're drawing our energy diagram, we're going to have the reaction progress along the X. Access and the potential energy along the Y access. Okay. And so let's recall that change in entropy. Our delta H. Is the difference in energy between products and reactant. And looking at our table here, we see that the change in entropy is negative, which means it is eggs A thermic. Alright. So we see both of these here are negative and so they are eggs. Ah thermic. And when we have an exotic thermic reaction, this signifies that the reactant are higher in energy than the products. Okay, so for our second step, since we're doing the sequence of step two and step three, we know our reactant is going to be higher in energy than our product. So let's go ahead and reflect that here. So step two is reflected by oh Plus 02. This is our reactant and we're going to go up and then down to step three. Okay, so let's take a pause here. So our energy for the reactant is higher than the products. Alright, so remember that activation energy is the difference in energy between reactant and transition state. Okay, so for step two, we see in the table here that we have an activation energy of 16 kg joules per mole. So that's going to be reflected here. This is our activation energy. Alright, so we'll go ahead and put 16 Because it's kind of hard to put it inside. So we'll put it here. So 16 is our activation energy which means that our change in entropy here. Okay, is going to be that negative 106.5. All right, So now that is for step two, Step three. Now we have our we have 03 plus and oh is now our reactant and it is also eggs a thermic. So it's going to have its react mints higher than its products. And we're going to go down here and our product is an 02 plus 02. Okay, so let's go ahead and do the same thing. Our activation energy here is 18. All right. And that means our change in entropy here, Is that negative .63. Let me try to write that a little bit clearer. So negative 84.63. Okay, so here remember the activation energy is the energy needed to reach this transition state and it's the minimum amount of energy molecules needed in order to react and produce products. And so for our energy diagram showing the sequence for Step two and three, that is what we have reflected here. Okay, so reflected our activation energy and our change in entropy ease. And that is it for this problem, I hope this was helpful.

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