Consider the following reaction: CH4+Cl ·→·CH3+HCl . a. Use curved arrows to show the movement o

Consider the following reaction: CH4+Cl ·→·CH3+HCl . a. Use...

Key Concepts

Radical Reaction Mechanism

This concept refers to a type of chemical reaction that involves species with unpaired electrons called radicals. The mechanism typically includes initiation, propagation, and termination steps, and it is characterized by single-electron transfers rather than the typical two-electron processes seen in polar reactions. Understanding radical reaction mechanisms helps in predicting reaction intermediates and the overall kinetics of the process.

Curved Arrow Notation

Curved arrow notation is a graphical convention used to depict the movement of electrons during chemical reactions. In mechanisms, curved arrows indicate how electrons are transferred from one atom or bond to another, especially in processes involving radicals where single-electron transfers are critical. This notation is essential for visualizing and rationalizing the changes in electron distribution that occur during a reaction.

Bond Dissociation Energy

Bond dissociation energy (BDE) is the amount of energy required to break a specific chemical bond homolytically, resulting in the formation of radicals. It is a key concept when estimating reaction enthalpies (?H°) in radical processes, as the energy changes involved in breaking and making bonds determine the overall thermodynamic favorability of a reaction.

Energy Diagrams

Energy diagrams provide a visual representation of the potential energy changes throughout a chemical reaction. They typically show the energy levels of reactants, transition states, and products along the reaction coordinate. These diagrams help in understanding the kinetic barriers (activation energy) and the thermodynamic properties (exothermicity or endothermicity) of a reaction.

Activation Energy in Reversible Reactions

Activation energy is the minimum amount of energy required for a reaction to proceed via its transition state. In reversible reactions, both the forward and reverse processes have their own activation energies. The relationship between these activation barriers is influenced by the overall reaction enthalpy, and understanding this relationship is crucial for analyzing the kinetics and dynamic equilibria of reversible chemical reactions.

Transcript

00:01 Okay, we have got methane, ch4, plus a chlorine radical, going to a methane radical, or ch3 radical, i should say, and a hcl.

00:16 And we're asked to use curved arrows to show the movement of electrons in this radical reaction, so i'm going to redraw.

00:22 I'm going to draw this as h3c with a bond to hydrogen.

00:28 So we need to break that bond, so we're going to want to draw it.

00:32 Then we'll draw our chlorine radical.

00:35 And we're abstracting a hydrogen and a radical reaction.

00:38 So we'll draw a single barbed arrow from the chlorine radical to empty space.

00:43 And then we'll meet that point with a single arrow from the carbon hydrogen bond.

00:52 That represents the forming of the chlorine hydrogen bond.

00:55 And then also breaking halfway of the carbon hydrogen bond.

00:59 The other half gets deposited on carbon.

01:02 And so that's going to be the curved arrows that show the movement of the reaction, which will give us the following products.

01:12 We've already seen this.

01:14 But here we go.

01:15 Okay, calculate delta h using the bond association energy in table 6 .2.

01:20 So what's going on? we're breaking an h3c hydrogen bond.

01:27 And we're forming an hcl bond.

01:32 Okay.

01:32 So we need to do bonds that we're breaking, the sum of all the bonds we're breaking, minus the sum of all the bonds that we're forming in terms of bond association energy.

01:47 So according to our bond association energy chart, table 6 .2, a ch3 to hydrogen bond is worth 104 killer calories per mole.

01:59 That is, it costs 104 killer calories.

02:03 Calories per mole to break a ch bond.

02:05 And to break a hcl bond, it costs 103 kilocals per mole.

02:17 Okay.

02:18 So our formula then is the sum of all the bonds are breaking, which is just this one here.

02:24 So 104 minus the sum of the bonds we're forming, which is this 103.

02:29 So minus 103...