The compounds CCl4 and H2 O do not react with each other. On...

The compounds $\mathrm{CCl}_{4}$ and $\mathrm{H}_{2} \mathrm{O}$ do not react with each other. On the other hand, silicon tetrachloride reacts with water according to the equation $$ \mathrm{SiCl}_{4}(l)+2 \mathrm{H}_{2} \mathrm{O}(I) \longrightarrow \mathrm{SiO}_{2}(s)+4 \mathrm{HCl}(a q) $$ Discuss the importance of thermodynamics and kinetics in the reactivity of water with $\mathrm{SiCl}_{4}$ as compared with its lack of reactivity with $\mathrm{CCl}_{4}$.

The compounds $\mathrm{CCl}_{4}$ and $\mathrm{H}_{2} \mathrm{O}$ do not react with each other. On the other hand, silicon tetrachloride reacts with water according to the equation
$$
\mathrm{SiCl}_{4}(l)+2 \mathrm{H}_{2} \mathrm{O}(I) \longrightarrow \mathrm{SiO}_{2}(s)+4 \mathrm{HCl}(a q)
$$
Discuss the importance of thermodynamics and kinetics in the reactivity of water with $\mathrm{SiCl}_{4}$ as compared with its lack of reactivity with $\mathrm{CCl}_{4}$.

Key Concepts

Thermodynamics

This concept deals with the energy changes associated with a chemical reaction. A reaction is thermodynamically favorable if it leads to products that are lower in free energy compared to the reactants, meaning the process is exergonic. In the context of reaction with water, thermodynamics explains why certain compounds can, in principle, form more stable products through hydrolysis while others cannot, despite the availability of water as a reactant.

Kinetics

Kinetics is concerned with the rate at which a reaction proceeds and the energy barrier (activation energy) that must be overcome for the reaction to occur. Even if a reaction is thermodynamically favorable, a high activation energy can render the reaction effectively non-occurring under given conditions. Therefore, kinetic factors explain the lack of observable reactivity in cases where reactants might otherwise have an energetically favorable outcome.

Electrophilicity and Bond Polarity

Electrophilicity refers to the tendency of a chemical species to attract electrons, often due to bond polarization. In compounds where a central atom is significantly polarized, the electrophilic center can be attacked by nucleophiles like water, facilitating reactions such as hydrolysis. When the central atom is not sufficiently polarized or is shielded by strong bonds, water molecules do not interact readily, leading to a lack of reactivity.

Hydrolysis Mechanism

Hydrolysis involves the cleavage of bonds through the addition of water. The mechanism relies on both thermodynamic favorability—where the resulting products are energetically lower—and suitable kinetic pathways that allow a water molecule to successfully attack the reactive site of a molecule. The differences in bond strength and electronic configurations between various compounds determine whether water can initiate a rapid and complete hydrolysis reaction.

Transcript

00:01 Carbon tetrachloride does not react with water, yet silicon tetrachloride does in accordance with the reaction i've written right here.

00:09 We are asked in this problem to discuss the importance of thermodynamics and kinetics in the reactivity of water with silicon tetrachloride and the lack of reactivity with carbon tetrachloride.

00:23 Okay, so i'm going to write the ionic equation for this.

00:34 So bear with me while i copy this down again.

00:54 Sulfuric acid is a strong acid, so this will be dissociated.

01:02 And then we can calculate our delta h by looking up our values as follows.

01:07 Our enthalpy change.

01:10 911 times 1 plus 4 times 0 and 4 times my negative 167.

01:33 We'll subtract from that 1 times negative 687 plus 2 times negative 286.

01:52 And my delta h for this will equal negative 320 kilojoules.

02:01 My delta s, so this is favorable because it's negative.

02:10 Then let's do our delta s and that will be, let me go down a little bit.

02:23 Whoops, my delta s will equal, let me jot this down, 1 times 42 plus 4 times 0 plus 4 times 57 minus 1 times 240 plus 2 times 70.

03:12 Equal negative 110 joules per kelvin.