Materials & Heat

What is mass?

A measure of the amount of matter (“stuff”) in a substance; scalar; SI unit: kilogram (kg).

What is the atomic mass scale?

A scale used to compare atomic masses; unit: atomic mass unit (u), defined as 1/12 the mass of carbon-12.

What is a mole?

The amount of substance containing as many particles as there are atoms in 12 g of carbon-12.

What is Avogadro’s number?

NA: number of particles per mole.

Relationship between molar mass and atomic/molecular mass?

Numerical value in g/mol equals the atomic/molecular mass in u.

Example mentioned for moles?

Calculate mass of 1 mol of hydrogen gas.

Example involving gemstones?

Find (a) number of carbon atoms in the Hope diamond, (b) number of Al₂O₃ molecules in the Rosser Reeves ruby.

What is mass density?

Density = mass / volume; scalar; SI unit: kg/m³.

Example given?

For a man weighing 690 N with 5.2×10⁻³ m³ of blood:
(a) find blood’s weight;
(b) express as percent of body weight.

What is temperature?

A physical property indicating “hotness”; if two objects have same temperature, no heat flows between them.

SI unit of temperature?

Kelvin (K).

What is heat?

Energy that flows spontaneously from higher-temperature to lower-temperature bodies; SI unit: joule (J).

What is the Celsius scale based on?

Ice point (0°C) and steam point (100°C), using expansion of mercury.

What is the Kelvin scale?

Absolute scale based on absolute gas pressure.

Absolute zero temperature in Celsius?

–273.15°C.

Why can Celsius and Kelvin be interchanged for temperature differences?

Because the size of a degree is the same for both.

What is linear thermal expansion?

Increase in length of a solid rod due to temperature increase.

What quantity determines expansion?

The coefficient of linear expansion.

Example given?

How much space to leave in a sidewalk (from 25°C to 38°C) for thermal expansion.

What is a bimetallic strip used for?

Thermostats.

What is specific heat capacity?

Heat required to raise 1 kg of a substance by 1 K; unit: J kg⁻¹ K⁻¹.

Example given?

A 65-kg jogger generates 8.0×10⁵ J in 30 min — find temperature increase if heat were not removed.

What happens to temperature during a phase change?

Temperature does not change (thermal equilibrium).

What is latent heat?

Heat required to change phase of a substance.

What is specific latent heat?

Heat required to change the phase of 1 kg of a substance without temperature change; unit: J/kg.

Conceptual spaghetti example?

Whether vigorous or gentle boil uses less energy (gentle boil is best).

Example given?

Ice at 0°C into lemonade at 27°C → find minimum mass of ice required so some remains after equilibrium.

What principle is used in calorimetry?

Heat lost by hot objects = heat gained by cold objects (if no loss to surroundings).

Example given?

Aluminium calorimeter with water; unknown metal added; find specific heat of unknown material.

What are the three heat transfer mechanisms?

Conduction, convection, radiation.

What is conduction?

Heat transfer through a material without bulk motion, via molecular collisions.

Factors affecting conducted heat?

Time, temperature difference, cross-sectional area, material, length.

What is thermal conductivity?

Quantifies conduction ability; unit: W/m/K.

Example given?

Heat conducted through a house wall of area 35 m² with conductivity 0.030 W/m/K over one hour

What is convection?

Heat transfer by bulk motion of a fluid.

Why do density differences cause convection?

Hot fluid is less dense → rises; cold fluid is more dense → sinks.

Example: Why baseboard heaters near floor?

To warm air that rises, driving convection currents.

Example: Why refrigerator coils at top?

Cold air sinks, aiding circulation.

What are “thermals”?

Rising warm air currents used by glider pilots to gain altitude.

What is forced convection?

Convection enhanced by fans, pumps, or motion (e.g., engine cooling, home heating).

How does foam insulation reduce heat loss?

Minimizes convection currents inside the insulation.

What is radiation?

Energy transfer by electromagnetic waves.

Relationship between absorbing and emitting?

Good absorbers are also good emitters.

Examples of radiation?

Sunlight reaching Earth; heat from an open fire.

Why wear light colours on hot days?

They reflect more radiation, absorbing less heat.

How does a thermos flask reduce heat transfer?

• Conduction: minimized by glass + vacuum
• Convection: prevented by vacuum
• Radiation: reduced by silvered surfaces

How does a halogen cooker work?

Emits electromagnetic energy that passes through ceramic and is absorbed by the pot bottom.

What topics were covered in Topic 7?

• Mass, moles & density
• Temperature & heat definitions
• Celsius & Kelvin scales
• Thermometer calibration
• Effects of heat
• Thermal expansion
• Heat capacities
• Latent heat
• Heat transfer: conduction, convection, radiation