Phases of Matter - AP Chemistry

Freezing point depression refers to the phenomenon that occurs when the freezing point of a solution is decreased due to the presence of ions or molecules. The freezing point depression is given by the formula:

refers to the van't Hoff factor, which is the number of ions created by dissolving a single molecule of the solute. In this case, the van't Hoff factor is two because HCl will create two ions per molecule in solution.

referes to the molality, which is the moles of solute per kilogram of solvent. We can rewrite our equation in these terms:

We know all of these terms, allowing us to solve:

This tells us that the freezing point of the solution is 11.16 degrees less than the freezing point of pure water.

Adding salt to water raises its boiling point. This allows the water to get hotter before evaporating. Boiling point elevation is a colligative property. Thus the increase in boiling point is proportional to the number of dissolved particles in solution, not the type of dissolved particles.

By definition, viscosity is the measure of a liquid's resistance to flow. If a liquid has a high resistance to flow, it has a high viscosity. It may not necessarily have a high boiling point or melting point, nor be easily soluble in other liquids.

Vapor pressure relates to the molecules' ability to escape from their liquid form into a gaseous state. The weaker the intermolecular forces, the greater the vapor pressure (VP). Liquids with hydrogen bonding general have high VP. Bigger and longer molecules have larger VP then smaller ones. Methane does not hydrogen bond, and it is a relatively small molecule, thus many molecules will have enough energy to break the weak intermolecular forces and enter the gaseous phase. Both water and methanol can hydrogen bond. Propane has weak bonds like methane, but it is a larger molecule and will thus have a lower vapor pressure.

A solid is defined as having a definite shape and definite volume. A liquid is defined as having a definite volume, but not a definite shape. A gas is defined as neither having a definite shape nor a definite volume.

Solids are defined as having definite shapes and volumes. The atoms in a solid touch one another and are fixed in rigid positions. Unlike liquids or gases, molecules inside a solid are not able to freely move past one another. Solids will retain their shape even when put in open atmospheres.

Aluminum is not a high-density metal. You may figure this out by comparing aluminum's density (2.7 g/mL) to the density of other metals. Aluminum is very lightweight compared to other metals, making it ideal for the construction of things like airplanes.

Aluminum is a good conductor of heat and electricity. It is ductile, meaning it can be turned into wire, and it is malleable, meaning it can be made into sheets.

Solids have well defined shapes because their atoms are held tightly together, only allowing localized movement. Because a solid's atoms are so close together, solids are incompressible. There so little space between atoms that they can't get any closer together. The reason a solid's atoms are so close together is they experience strong intermolecular forces, resulting in high stability. Solids can either be crystalline or amorphous in structure. Crystalline structure is regimented and grid-like, while amorphous has no regular, repeating pattern of atoms.

A crystalline solid is made up of a repeating pattern of atoms called a crystal lattice. Atoms moving about randomly, and taking the shape of their container are descriptions of fluids (liquids and gasses).

Dissolving a solute in a solvent increases the number of dissolved particles per mass of solvent. Freezing point depression is a colligative property of solutions, and will decrease as the molality of the solution increases. Boiling point and osmotic pressure increase as the molality of the solution increases. Temperature is unaffected by the dissolution of solutes in a solvent.

The salt decreases the freezing point of the water. Upon addition of salt to icy roads and sidewalks, the ice melts, making it safer to drive and walk. Freezing point depression is a colligative property and depends on the number of dissolved particles, not the type of particles. Thus, sugar would also decrease the freezing point of ice. The amount the freezing point decreases is proportional to the number of dissolved solutes in the solution.

Crystals, or crystalline solids consist of repeated, regular pattern of atoms known as a crystal lattice. Amorphous solids do not have a lattice, and consist of a mass of atoms without a repeated pattern.

Gases with high higher molecular weights are going to move at slower velocities. At a given temperature, all gases have the same average kinetic energy. For this to remain true, larger molecules must move slower since they have greater masses.

The gas to diffuse quickest will have the smallest molecular weight. In this case, that gas is hydrogen.

There are six primary properties of gases: expansion, fluidity, low density, compressibility, diffusion, and effusion.

Expansion suggests that gases have no defined shape and will expand to fill a given space, without significant intermolecular interaction. Fluidity is a property of both gases and liquids and describes the relatively low attraction between particles. This allows the gas molecules to move past one another, creating the "fluid" nature of the gas. Low density of gases is linked to gas expansion. Gases will expand to the greatest extent possible, resulting in low mass per unit volume ratios. Compressibility is also linked to expansion and the indefinite shape of the gas, essentially suggesting that the distance between particles can be reduced if pressure is increased. Diffusion and effusion are both linked to the movement of gases. Diffusion means that gases can spread out and mix within a given space, while effusion means that gases can pass through a small opening at a given rate.

Some of these properties are unique to gases, while others are shared between gases and liquids. Gases have virtually no physical properties in common with solids.

Each gas in a mixture of gases exerts its own pressure independently of the other gases present; therefore the pressure of each gas within a mixture is called the partial pressure of the gas.

Dalton's law of partial pressures states that the total pressure of a mixture of gases is equal to the sum of the partial pressures of the component gases. This can be expressed mathematically as follows:

Boyle's law and Gay-Lussac's law can help determine pressure in varying volumes and temperatures, respectively, but can only be useful with regard to the total pressure of the system. The second law of thermodynamics is not related to gas properties, and states that the entropy of the universe is constantly increasing.

Gases are able to effuse though small pinhole openings, and diffuse into empty spaces from high to low concentrations. The kinetic energy of gas molecules is dependent on temperature. Higher temperatures cause in increase in the kinetic energy of the particles.

Gases have very low densities. Density is a measure of mass per unit volume. Since the gas molecules are spread out over a much larger distance compared to liquids and solids, their densities are very low.

The partial pressures of each gas are not dependent on their masses, but the total number of moles of gas in the container. Since we know how much pressure the fluorine gas exerts on the container, we can solve for the molar fraction of fluorine gas in the container.

In other words, 62.5% of the gas in the container is fluorine gas. Knowing this, we can solve for how many moles of neon gas are in the container.

50 grams of fluorine gas is equal to 1.32 moles of fluorine gas. If this molar amount accounts for 62.5% of the gas in the container, we can solve for the total number of moles in the container:

Since there are only two gases in the container, we can solve for the number of moles of neon gas in the container.

Since there are .79 moles of neon gas, we can multiply by the molar mass and find the toal mass of the neon gas in the container:

Use Dalton's law of partial pressure:

Where is the partial pressure of oxygen and is the mole fraction of oxygen. Plug in known values and solve.

Divide each component by their molecular weight to obtain the number of moles. The hydrogen gas has the most moles that occupy the same volume. Remember that of the answer choices, hydrogen, and oxygen are both diatomic gasses, which needs to be taken into account when calculating the number of moles. For simplicity, let's assume we have 1L of each gas.

As an example, let's calculate the number density for oxygen to show that it is indeed less than that for hydrogen.