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Chemistry & Chemical Reactivity

10th Edition
John C. Kotz + 3 others
ISBN: 9781337399074

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BuyFindarrow_forward

Chemistry & Chemical Reactivity

10th Edition
John C. Kotz + 3 others
ISBN: 9781337399074
Textbook Problem

Dihydroxyacetone is a component of quick-tanning lotions. (It reacts with the amino acids in the upper layer of skin and colors them brown in a reaction similar to that occurring when food is browned as it cooks.)

  1. (a) Use bond dissociation enthalpies to estimate the enthalpy change for the following reaction. Is the reaction exothermic or endothermic?

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  1. (b) Are dihydroxyacetone and acetone polar molecules?
  2. (c) A proton (H+) can be removed from a molecule of dihydroxyacetone with strong bases (which is in part what happens in the tanning reaction). Which H atoms are the most positive.

(a)

Interpretation Introduction

Interpretation: The enthalpy change for the given reaction should be estimated by using bond dissociation enthalpies. The given reaction exothermic or endothermic should be identified.

Concept Introduction:

Bond dissociation enthalpy:

Bond energy or more correctly the bond dissociation enthalpy is the enthalpy change when breaking a bond in a molecule with the reactant and products in the gas phase.

The process of breaking bonds in a molecule is always endothermic, so ΔrH for bond breaking is always positive.

    ΔrH0 = ΔH(bonds broken)-ΔH(bonds formed)

Explanation

The enthalpy change for given reaction estimated as follows by using bond dissociation enthalpy.

The two C-H bonds, one O=O are broken. The two O-C bonds and two H-O bonds are formed in the reaction.

    ΔrH0 = ΔH(bonds broken)-ΔH(b

(b)

Interpretation Introduction

Interpretation: The given molecules should be identified that whether they are polar or non-polar.

Electronegativity: It is defined as the capacity of the atom to abstract the pair of electrons towards itself results to have high negative charge.

Polar molecule: The molecule with atoms bonded with different electronegativity. Dipole moment is used to measure the polarity of the molecule.

Polarity of a molecule is measured in term of dipole moment.

Dipole moment for a polar molecule is non-zero and for a non-polar molecule dipole moment is zero.

(c)

Interpretation Introduction

Interpretation: The most positive H atoms in molecule dihydroxyacetone should be identified.

Electronegativity: It is defined as the capacity of the atom to abstract the pair of electrons towards itself results to have high negative charge.

Polar molecule: The molecule with atoms bonded with different electronegativity. Dipole moment is used to measure the polarity of the molecule.

Polarity of a molecule is measured in term of dipole moment.

Dipole moment for a polar molecule is non-zero and for a non-polar molecule dipole moment is zero.

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