Phys: Particle model of matter

What is the formula for density, including standard units and symbols?

$\text{Density } (\rho) = \frac{\text{mass } (m)}{\text{volume } (V)}$, where density is in $\text{kg/m}^3$, mass is in $\text{kg}$, and volume is in $\text{m}^3$.

How do particle arrangement and energy differ between solids, liquids, and gases?

Solids: Strong forces hold particles close in a fixed, regular arrangement with low energy, vibrating in fixed positions; Liquids: Weaker forces allow particles to stay close in irregular arrangements, moving past each other in random directions at low speeds; Gases: Almost no forces, particles have high energy and move freely in random directions at high speeds.

How do you measure the density of a regular solid object?

1) Measure mass using a balance; 2) Measure dimensions (length, width, height) with an appropriate tool (e.g., ruler) and calculate volume using the shape's formula; 3) Calculate density using $\rho = \frac{m}{V}$.

Describe the experimental method for measuring the density of an irregular solid object using a eureka can.

1) Measure the mass of the object using a balance; 2) Submerge the object in a eureka can filled with water up to the spout; 3) Collect and measure the volume of displaced water using a measuring cylinder (this equals the object's volume); 4) Calculate density using $\rho = \frac{m}{V}$.

Describe the step-by-step practical procedure to determine the density of a liquid.

1) Place a measuring cylinder on a balance and zero it; 2) Pour $10\text{ ml}$ of liquid into the cylinder and record its mass; 3) Repeat in $10\text{ ml}$ increments, recording total mass and total volume each time; 4) Calculate density for each reading using $\rho = \frac{m}{V}$ ($1\text{ ml} = 1\text{ cm}^3$); 5) Calculate an average of the results.

What is internal energy, and how is it stored within a system?

Internal energy is the total energy stored by the particles that make up a system, consisting of the sum of their total kinetic energy stores and potential energy stores.

How does heating affect the internal energy of a system?

Heating transfers energy to the particles (increasing their kinetic or potential stores), which increases the overall internal energy of the system and leads to either a temperature change or a change of state.

Why is a change of state classified as a physical change rather than a chemical change?

Because the substance recovers its original properties if the change is reversed, no new substance is formed, and mass is conserved (the number of particles remains unchanged).

What occurs at the particle level during a change of state when a substance is heated enough to melt or boil?

The particles gain sufficient energy in their kinetic stores to overcome and break the intermolecular bonds holding them together.

What happens to energy and temperature during a change of state when heating or cooling a substance?

Energy transferred by heating goes into breaking or forming bonds between particles rather than changing temperature; flat sections on heating and cooling graphs show where internal energy changes during state transitions at a constant temperature.

What is the definition of specific latent heat?

The amount of energy required to change the state of $1\text{ kg}$ of a substance without changing its temperature.

What is the distinction between specific latent heat of fusion and specific latent heat of vaporisation?

Specific latent heat of fusion applies to changes of state between a solid and a liquid (melting or freezing); specific latent heat of vaporisation applies to changes between a liquid and a gas (boiling, evaporating, or condensing).

What formula links energy ($E$), mass ($m$), and specific latent heat ($L$)?

$E = m L$, where energy is in joules ($\text{J}$), mass is in kilograms ($\text{kg}$), and specific latent heat is in $\text{J/kg}$.

How is the temperature of a gas related to the kinetic energy of its particles?

The temperature of a gas is directly proportional to the average energy in the kinetic energy stores of its particles; higher temperatures mean higher particle speeds.

How do gas particles create pressure on the walls of a container?

Gas particles move randomly at high speeds and collide with container walls, exerting a net outward force at right angles to the surface per unit area.

How do changes in temperature and volume affect the pressure of a fixed mass of gas?

Increasing temperature increases particle speed and collision frequency, raising pressure at constant volume; increasing volume at constant temperature spreads particles out, reducing collision frequency and lowering pressure.

What relationship connects pressure ($p$) and volume ($V$) for a fixed mass of gas at a constant temperature?

Pressure and volume are inversely proportional ($p V = \text{constant}$), meaning as volume increases, pressure decreases proportionally.

How does a flexible container (such as a balloon) respond to changes in internal or external pressure?

Changes in external or internal pressure alter the net outward force at right angles to the container walls, causing it to expand or compress until internal and external pressures balance.

How does doing work on a gas mechanically affect its internal energy and temperature?

Doing work on a gas (e.g., pushing a bike pump plunger against internal gas pressure) transfers energy to the kinetic energy stores of its particles, increasing internal energy and raising the temperature.