Physical Chemistry : Properties of Solids

Study concepts, example questions & explanations for Physical Chemistry

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Example Questions

Example Question #1 : Properties Of Solids

Which of the following is true regarding solids?

Possible Answers:

More than one of these

Solids have high entropy

Each solid requires a unique amount of energy to separate the molecules

None of these

Correct answer:

Each solid requires a unique amount of energy to separate the molecules

Explanation:

There are three main phases: solids, liquids, and gases. Solids molecules are closely packed in an organized, lattice structure, liquid molecules are more spread apart and more disorganized, and gas molecules are spread even farther apart from each other and are extremely disorganized. Each type of solid is made up of unique type of atoms. For example, magnesium metal is made up of magnesium atoms whereas copper metal is made up of copper atoms. Since they are made up of unique atoms, different types of solids have different interactions between atoms. Some have strong interactions whereas others have very weak interactions; therefore, the energy required to break these interaction and separate the atoms/molecules (melt) is different for each solid. 

Recall that entropy is the level of disorder in a system. As mentioned, solids are highly organized structures; therefore, they will have the lowest entropy.

Example Question #2 : Phases And Properties Of Matter

You freeze a sample of nitrogen. Compared to the reactant, the end product has __________ density and __________ mass.

Possible Answers:

the same . . . the same

a lower . . . the same

a higher . . . a higher

a higher . . . the same

Correct answer:

a higher . . . the same

Explanation:

Freezing the is process of converting a liquid to a solid. This question is asking about the freezing process of liquid nitrogen to solid nitrogen; therefore, the end product of the reaction is solid nitrogen. Recall that solids are more tightly packed. This means that the volume taken up by the molecules in solid is lower than in liquid; therefore, solids generally have a lower volume. Mass, on the other hand, depends on the number of molecules present. Phase changes do not alter the amount of molecules present. For example, the end product in this question (solid nitrogen) will have the same amount of molecules as its liquid counterpart; therefore, the mass doesn’t change when the phase changes.

Density is defined as follows.

Since its volume decreases and the mass stays the same, a solid will have a lower density than liquid. Note that water is an exception to this general rule, as solid ice has a lower density (higher volume) than the same mass of liquid water. This is due to the arrangement of its hydrogen bonds throughout its crystalline structure. 

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