
Concept explainers
Calculate the number of atoms in the universe. The following steps will guide you through this calculation:
a. Planets constitute less than 1% of the total mass of the universe and can, therefore, be neglected. Stars make up most of the visible mass of the universe, so we need to determine how many atoms are in a star. Stars are primarily composed of hydrogen atoms and our Sun is an average-sized star. Calculate the number of hydrogen atoms in our Sun given that the radius of the Sun is
(Hint: Use the volume and the density to get the mass of the Sun.)
b. The average galaxy (like our own Milky Way galaxy) contains
c. You can hold

Interpretation:
The number of hydrogen atoms in the sun and the number of atoms in a random galaxy are to be determined. Also, the number of hydrogen atoms in the universeis to be compared with the number of atoms that can be held in a hand.
Concept Introduction:
Density is the ratio of the mass of a substance to its volume.
The volume of a sphere is
Mole is the unit of the amount of a substance. It relates number of particles to the molar mass.
One mole of a substance contains Avogadro’s number (
It also relates to the molar mass of a substance in grams. The weight of one mole of a substance is equivalent to its molar mass in grams.
It is known that
Answer to Problem 56E
Solution: a)
Explanation of Solution
a) The number of hydrogen atoms present in the sun.
The radius of the sun is
The number of hydrogen atoms present in the sun is calculated as:
Conversion of the radius of the sun from m to cm is as:
The volume of a sphere is
Substitute the values in the above equation:
Thus, the volume of the sphere is
The mass of hydrogen in sun using the values of density and volume is calculated as:
Substitute the values in the above equation:
Therefore, the mass of hydrogen in sun is
The number of atoms of hydrogen is calculated as follows:
Hence, the number of atoms in hydrogen are
b) The number of hydrogen atoms present in one galaxy and in universe.
The average galaxy consists of
The number of hydrogen atoms in one galaxy
Therefore, hydrogen atoms present in one galaxy are
The number of hydrogen atoms in the universe
Thus, the number of hydrogen atoms in universe is
c) Compare
The atoms which can be held in a hand are
The number of atoms that can be held in a hand are
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Chapter 3 Solutions
Bundle: Chemistry in Focus, Loose-leaf Version, 7th + OWLv2, 1 term (6 months) Printed Access Card
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