Homework 74

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1.64, 10.66

Question 1.64: Write the isotopic symbols in the form ^A_ZX for each isotope.

The oxygen isotope with 9 neutrons.
The neon isotope with 10 neutrons.
The chlorine isotope with 18 neutrons.
The carbon isotope with 8 neutrons.

Solution

Strategy:

Identify each element’s atomic number (number of protons).
Find the atomic mass of each element by adding the number of protons and the number of neutrons.
Properly write the isotopic symbol of each element by placing the atomic mass as the superscript and the atomic number (number of protons) as the subscript.

Atomic Numbers (Number of Protons):

Oxygen: 8 protons

Neon: 10 protons

Chlorine: 17 protons

Carbon: 6 protons

Atomic Mass:

Oxygen: 8+9=17

Neon: 10+10=20

Chlorine: 17+18=35

Carbon: 6+8=14

Isotopic Symbols:

Oxygen: ¹⁷₈O

Neon: ²⁰₁₀Ne

Chlorine: ³⁵₁₇Cl

Carbon: ¹⁴₆C

Question 10.66: In order to obtain the smallest possible amount of heat in which there is a large decrease in the number of moles of gas, should you carry out the reaction under conditions of constant volume or constant pressure? Explain.

Solution: In order to obtain the smallest amount of heat in which there is a large decrease in the number of moles of gas, you should carry out the reaction under conditions of constant volume. According to Avogadro’s Law (V₁/n₁=V₂/n₂), volume is directly proportional to the number of gas molecules. Thus, as the volume of the gas increases, the number of moles increases. Likewise, as the volume of the gas decreases, the number of moles decreases. As a result, if you wanted to obtain the smallest amount of heat in which the number of moles decreases, you should carry out the reaction with a decreasing constant volume.