   Chapter 21, Problem 129SCQ

Chapter
Section
Textbook Problem

Comparing the chemistry of carbon and silicon.(a) Write balanced chemical equations for the reactions of H2O(ℓ) with CH4 (forming CO2 and H2) and SiH4 (forming SiO2 and H2).(b) Using thermodynamic data, calculate the standard free energy change for the reactions in (a). Is either reaction product-favored at equilibrium?(c) Look up the electronegativities of carbon, silicon, and hydrogen. What conclusion can you draw concerning the polarity of C—H and Si—H bonds?(d) Carbon and silicon compounds with the formulas (CH3)2CO (acetone) and [(CH3)2SiO]n (a silicone polymer) also have quite different structures. Draw Lewis structures for these species. This difference, along with the difference between structures of CO2 and SiO2, suggests a general observation about silicon compounds. Based on that observation, do you expect that a silicon compound with a structure similar to ethene (C2H4) exists?

(a)

Interpretation Introduction

Interpretation:

Compare the chemistry of carbon and silicon and the balanced chemical equation for the reaction of H2O with CH4 and SiH4 has to be written.

Concept introduction:

Carbon and silicon both belongs to group 4A of the periodic table. Since they belong to same group, the chemistry of both these elements are somewhat similar. Both are non-metals and have similar density. Both carbon and silicon have same chemical properties. For example, both silicon and carbon forms hydrogen gas with water.

A balanced chemical equation occurs when the number of atoms in reactant side is equal to the number of atoms in the product side.

Explanation

Both carbon and silicon have same chemical properties. For example, both silicon and carbon forms hydrogen gas with water.

CH4 forms CO2(g) on reaction with water.

SiH4 forms SiO2(s) on reaction with water.

The balanced chemical equation for the reaction of H2O(l) with CH4 is,

CH4(g)+2H2O

(b)

Interpretation Introduction

Interpretation:

The standarad free energy change for the given reaction has to be determined and check whether the reaction is product favoured at equilibrium or not.

Concept introduction:

Carbon and silicon both belongs to group 4A of the periodic table. Since they belong to same group, the chemistry of both these elements are somewhat similar. Both are non-metals and have similar density. Both carbon and silicon have same chemical properties. For example, both silicon and carbon forms hydrogen gas with water.

Standard Gibb’s energy change can be calculated using the following equation,

ΔrG°=nΔfG°(products)nΔfG°(reactants)

At equilibrium the reaction is product favoured if the Gibb’s energy change value is negative.

(c)

Interpretation Introduction

Interpretation:

The possible coclusion concerning to the polarity of CHandSiH has to be stated using the electronegativites of carbon, silicon, and hydrogen.

Concept introduction:

Polar covalent bond involves an unequal sharing of electrons between two bonded atoms; it creates a partial separation of charge and a dipole moment.

Covalent bonds are polar, if there is a difference in electronegativity between the bonded atoms.

(d)

Interpretation Introduction

Interpretation:

Lewis structure for acetone and the given silicon polymer has to be drawn.

Concept introduction:

Lewis structures are diagrams that represent the chemical bonding of covalently bonded molecules and coordination compounds.

It is also known as Lewis dot structures which represent the bonding between atoms of a molecule and the lone pairs of electrons that may exist in the molecule.

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