Study "States of matter", a flashcard deck on FORKSAI.
THEORETICAL: Explain why a gas can change directly to a solid, even though it's not always shown in simple state change diagrams.
A gas can change directly to a solid through a process called deposition or desublimation. This occurs when gas particles lose enough kinetic energy to form a solid structure without first passing through a liquid phase, typically under specific temperature and pressure conditions.
THEORETICAL: Why do changes 1 and 3 (condensation and freezing, respectively) involve particles moving closer together?
Changes like condensation (gas to liquid) and freezing (liquid to solid) involve particles moving closer together because energy is removed from the substance. As particles lose kinetic energy, their movement slows down, allowing intermolecular forces to pull them into more ordered, compact arrangements.
THEORETICAL: Explain why changes 2 and 4 (boiling/evaporation and melting, respectively) involve particles moving further apart.
Changes such as boiling/evaporation (liquid to gas) and melting (solid to liquid) involve particles moving further apart because energy is supplied to the substance. This added energy increases the kinetic energy of the particles, enabling them to overcome intermolecular forces and move more freely, leading to increased separation.
THEORETICAL: Why do changes 3, 4, and 5 (freezing, melting, and condensation/evaporation) not all involve the release of energy?
Changes 3 (freezing) and 5 (condensation) involve the release of energy as particles come closer together and form stronger bonds. However, change 4 (melting) involves the absorption of energy to break bonds and allow particles to move further apart, not the release of energy.
THEORETICAL: In a diffusion experiment with ammonia and hydrogen chloride gases, why does a white deposit of ammonium chloride form closer to the hydrogen chloride source?
Ammonium chloride forms closer to the hydrogen chloride source because ammonia gas (NH3, Mr=17) has a lower relative molecular mass than hydrogen chloride gas (HCl, Mr=36.5). According to Graham's Law of Diffusion, lighter molecules diffuse faster, so ammonia travels a greater distance in the same amount of time before reacting with HCl.
THEORETICAL: Why does the smell of bromine eventually spread across a room after drops are placed on a table-top?
The smell of bromine spreads due to diffusion. After evaporation, bromine particles collide with air particles, move in a random way, and spread out to occupy the total available space. This continuous random motion and collision lead to the uniform distribution of bromine particles throughout the room.
DEFINITION: Define diffusion and explain why it provides strong evidence for the particle theory of matter.
Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration, resulting from their random motion. It provides strong evidence for the particle theory of matter because it demonstrates that particles are in constant, random motion and that there are spaces between them, allowing them to spread out and mix.
THEORETICAL: Explain why propane (C3H8) and carbon dioxide (CO2) diffuse at the same rate at room temperature and pressure.
Propane (C3H8) and carbon dioxide (CO2) diffuse at the same rate because they have the same relative molecular mass (Mr). Propane's Mr is 3(12) + 8(1) = 44, and carbon dioxide's Mr is 12 + 2(16) = 44. The rate of diffusion is inversely proportional to the square root of the relative molecular mass, so identical molecular masses result in identical diffusion rates.
THEORETICAL: Why do brown fumes of bromine vapour slowly spread through a covered gas jar when a drop of liquid bromine is placed at the bottom?
This phenomenon occurs because bromine molecules and the molecules in the air are always moving around randomly. The bromine molecules, initially concentrated at the bottom, collide with air molecules and gradually spread out due to their constant motion until they are uniformly distributed throughout the gas jar.
THEORETICAL: In a diffusion experiment with a porous pot, which gas (CO2, Cl2, CH4, or NO2) in the beaker will cause the water level at Y to rise, and why?
Methane (CH4, Mr=16) will cause the water level at Y to rise. This is because methane has a lower relative molecular mass than air (average Mr approx. 29). Lighter methane molecules will diffuse into the porous pot faster than the heavier air molecules diffuse out, increasing the pressure inside the pot and pushing the water level down in the pot and up at Y.