Heat and Temperature - SCI STAGE 9 S2A

Entire Unit 3: 3.1-3.6

Heat is the energy that flows from hotter regions to colder regions, it is the flow of energy from warmer to cooler places. It is a flow of energy due to temperature differences. It is the energy that moves.

What is heat?

It is the average energy (or speed) of particles in a substance.

What is temperature?

1. The mass of the atoms in the substance.

2. The speed/vibrations of the atoms in the substance.

3. The energy of the atoms in the substance.

What factors affect temperature?

Thermal energy is the total energy of particles in a substance. Thermal energy refers to the energy contained within a system that is responsible for its temperature (so energy of particles, or total energy). It is the random kinetic energy of particles in an object.

What is thermal energy?

• Heat is the FLOW OF ENERGY from hotter to colder places.

• Temperature is the AVERAGE ENERGY OF PARTICLES in a substance.

• Thermal energy is the TOTAL HEAT ENERGY inside an object.

• Heat is the energy moving from hot to cold, temperature shows how hot something is, thermal energy is the total heat energy.

What is the difference between heat, temperature and thermal energy?

1. Potential energy - energy at rest

2. Kinetic energy - energy in motion

3. Gravitational energy - energy in gravity/falling

4. Thermal energy - energy of heated particles

5. Sound energy

6. Light energy

7. Elastic energy

8. Heat energy - when the digestive system is turning the food into enzymes already, it can release heat energy

List the types of energy.

All of the particles that make up matter are constantly in motion. Particles of a solid will vibrate in fixed positions, particles of a liquid flow in motion, particles of a gas move freely, and particles of plasma move incredibly fast and freely.

What is the kinetic theory of matter?

All matter is made up of atoms that are moving, even solids have particles that are vibrating. The motion from the atoms gives the object energy, which is the thermal energy needed for heat transfer, creating temperature.

Explain why temperature depends on particle movement.

Dissipation is the spreading out of thermal energy. Dissipated energy is energy that spreads out into the surroundings and usually cannot be used to do useful work.

→ It is not lost, its just LESS USEFUL. Often, it is converted to heat, sound and friction.

What is dissipation?

Specific heat capacity is the amount of heat needed to raise the temperature of 1 kilogram of a substance by one degrees celsius.

Unit: J/kg x degree celsius.

It tells us how much heat energy is needed to make something get warmer.

-→ thats why the same heat causes DIFFERENT temperature CHANGES in different substances. they have difference specific heat capacity.

What is specific heat capacity?

1. If a material has a high specific heat capacity, it means it takes a lot of heat to raise its temperature (eg. water).

2. If it has a low specific heat capacity, it heats up quickly, like metals.

What does it mean if a substance has a high/low specific heat capacity?

It is relevant to the temperature and thermal energy of different things because it measures how much heat is needed to raise the temperature of an object.

Why is specific heat capacity relevant to temperature and thermal energy?

J/kg x degrees celsius

eg. water has a specific heat capacity of 4200 J/kg*C (replace the asterisk as a degree symbol), which means it needs 4200 joules of heat to warm it up by 1 degree celsius.

What is the unit of specific heat capacity?

Energy is never created nor destroyed, it can only be changed or transferred from one form to another. You cannot make energy from nothing. Energy always comes from something that already exists.

→ Energy may be changed from one form to another, but no energy is ever lost or destroyed. (eg. potential to kinetic energy).

State the law of conservation.

A Sankey diagram is a visual tool used to show how energy is transferred in a system (or transported). A bigger arrow in the diagram represents more energy. A downward pointing arrow represents wasted energy, while forward pointing arrows to the right represent useful energy.

• Input energy = energy that enters the system.

• The start of the main arrow is the input energy, also the total energy.

• Useful energy = energy that does the JOB that we WANT.

• Wasted energy = energy that is lost to things that we do NOT WANT. (eg. heat, sound, friction. depends on what is the output you desire though.)

Whereas: Conservation of energy is observed → Input energy = useful energy + wasteful energy (output energy).

→ The total energy in a closed system always stays the same.

What is a Sankey diagram?

When the volume is the same, the only difference would be due to the thermal energy already present within them. Other than that, when their volume is different, and their temperatures are the same, the one with the greater volume would have a higher thermal energy.

When the volume is the same of two same objects, what makes them different in terms of thermal energy?

Yes, they do. All liquids, gases and most solids expand when their temperature increases. This is called thermal expansion. This is why some bridges have short segments so that it allows for expansion when heated.

Do liquids, gases and solids expand when their temperature increases?

A thermometer can measure temperature because the substance of the liquid inside always expands (increases) or contracts (getting smaller, decreases) because of a change in temperature.

How does a thermometer work?

Celsius: -273.15

Fahrenheit: -459.67

Kelvin: 0K

What is the temperature of absolute zero/absolute cold in celsius, fahrenheit, and kelvin?

Celsius to F: 9/5 x C + 32

F to C: 5/9 x (F - 32)

K to C: K - 273

C to K: C + 273

How do you do the conversion of temperature units?

Heat transfer is the movement of heat energy from warmer objects to cooler ones. There are 3 main types of heat transfer: conduction, convection and radiation. Heat transfer will continue until both objects are at the same temperature, or in equilibrium.

What is heat transfer?

1. Conduction → needs medium, needs direct contact
   Conduction is when energy is transferred from a hotter region to a colder region in a substance, by the particles vibrating.
   eg. A metal is heated from one end and the particles in that end gains energy and vibrates. They will move through the metal from that end to the other. Another example is when a Bunsen burner is turned on, and a rod is placed over it. Heat transfer will occur from the flame to the heated end of the rod, and the energy will soon be transferred to the other end.
   Eg. Ironing clothes
   → Have direct contact = definitely conduction

2. Convection → needs medium, no direct contact
   Convection is the transfer of heat through fluids, that means liquids or gases. When part of a fluid is heated, it will become less dense and will rise. The colder parts will sink as its denser and get heated up. This moves heat around the substance and eventually will heat all of it up. Heat transfer is created as the movement of the fluid creates a convection current that moves heat through the fluid.
   Eg. Boiling water
   → As long as liquids/fluids are involved = definitely convection

3. Radiation → no medium, no direct contact
   Radiation can be described as the transfer of heat energy from an area of high temperature to an area of low temperature using waves. All objects above absolute zero can emit those waves, such as infrared radiation from a fire or the visible light from the sun.
   When an objects gives out or EMITS radiation, it cools down. This makes the surroundings hotter, as heat is also transferred to it. A medium is not needed for radiation, as it can travel through a vacuum.
   Eg. The sun shining down at us.
   → As long as no medium is required = definitely radiation

What are the types of heat transfer?

1. Conduction: ironing clothes, putting a metal spoon in hot soup, holding a hot cup of water
   OR: Touching a hot stove. (not recommended, burns eminent.) or cooking marshmallows

2. Convection: boiling water, hot air balloons, radiators heating up rooms
   OR: Blowing on a hot soup, AC, earth’s crust, cooking, land VS sea breeze.

3. Radiation: Sun shining, fireplace heat, microwave
   OR: Warmth from a light bulb, drying wet clothes under the sun, campfire

Give examples of heat transfer in daily life.

The main factors affecting heat transfer are the temperature difference between objects, the surface area involved, and the material's properties like its thermal conductivity.

Other factors include the distance between objects, the type of heat transfer (conduction, convection, radiation), and the geometry or thickness of the material. 

What are the factors affecting heat transfer?

The particles will gain energy, move faster, and spread apart, making the fluid less dense. Because the warmer fluid is lighter, it rises due to buoyancy in convection, the cooler, denser fluid from above will then sink to replace the rising warm fluid. This creates the continuous circulation pattern known as a convection current.

What happens to the particles of a substance when it is heated?

1. Good: Black, dark, dull, rough and unreflective surfaces. Large surface area. (eg. iron, metals)

2. Bad: White, silver, shiny and reflective surfaces. Small surface area. (eg. aluminum foil, glass, silver)

What kinds of objects are good/bad emitters and absorbers of radiation?

This is because thermal energy from our hand has transferred away from our hands to the ice, making us feel cold.

Why do you feel cold when you hold ice?

Conductors → materials that transfer heat quickly

Insulators → materials that do not transfer heat quickly

In insulators, their particles are more tightly bound together, which means that their vibrations cannot spread as easily.
Eg. lunchbox insides are silver for preventing heat transfer so they reflect back on food, insides are made of insulating material.

What are conductors and insulators?

Evaporation is the escape of fast-moving particles from the surface of a liquid, thus causing the liquid to change into a gas as its particles get faster and farther away from each other.

What is evaporation?

Liquids change to vapour at temperatures below the boiling point.

A liquid changing into vapour is said to be evaporating. This process is called evaporation.

How do liquids change to vapour?

Evaporation:

• Occurs at any temperature

• Occurs at the surface

• No bubbles appear

Boiling:

• Occurs at a definite temperature — the boiling point

• Occurs within the liquid

• Bubbles appear

→ Evaporation and boiling both require latent heat of vaporization (thermal energy).

Difference between evaporation and boiling.

Cooling by evaporation is a process in which a liquid will evaporate, thus taking away energy from a heat source with a higher temperature, uses the thermal energy it gets for evaporation; and finally it will cause a cooling effect as the particles with the highest energy will now escape from the surface of the liquid and make the total thermal energy drop.

What is cooling by evaporation?

1. Fast-moving particles in liquid escape and become vapour;

2. While slow-moving particles in vapour stick back to the liquid.

3. The rate of evaporation (drying up) is a balance between the rate of escape and the rate of return.

→ Cooling by evaporation occurs when liquids evaporate; causing the highest energy particles to be turned into gas as they escape from the liquid, and thus decreasing the total thermal energy. This makes the temperature of the liquid drop, thus cooling whichever substance it is on, as the heat from that surface will now TRANSFER to the liquid as it is colder.
eg. Spraying perfume on your body, rubbing alcohol on your skin, after taking a bath, stepping out of a swimming pool, sweating

How does cooling by evaporation occur?

Sweat comes out from the pores, evaporates, thus taking energy away from the skin, so we feel cool. This is because heat transfer will occur where the liquid will get the energy for evaporating from our skin. The thermal energy on our skin will now decrease.

How does sweating cool the body?

Yes, they do. Different particles have DIFFERENT VELOCITIES, which causes parts of the liquid to have slower moving particles being left behind when it evaporates, causing the thermal energy to drop as only the fast moving particles, with the most energy (or KE, which stands for kinetic energy), will move away and decrease it.

1. Fast moving particles can escape from the liquid, as they have the highest KE

2. Medium moving particles can try to escape from the liquid, but they will get pulled back down into it as their KE is not high enough

3. Slow moving particles will stay in the liquid.

Do different particles in a liquid have different velocities (speeds)?

1. Temperature of the liquid
   As the temperature of the liquid increases, the rate of evaporation increases. This is because the energy of the liquid particles are higher, so evaporation occurs more easily as the particles can escape much easier.

2. Humidity of the air surrounding the liquid
   As the humidity of the air increases, the rate of evaporation decreases.
   If the air is humid, it is full of water vapour, and so it will make the water have a greater chance to just return back to the liquid, thus decreasing the rate of evaporation.

3. Increasing surface area of the liquid
   As the surface area of the liquid increases, the rate of evaporation increases.
   The larger the surface area, the more molecules can escape at the same time, so, it will increase the rate of evaporation.

4. Increasing air molecules around the liquid/Movement of air (breeze)
   As the number of air molecules around the liquid increases, or there is an increased movement of air, the higher the rate of evaporation.
   If there is a breeze, the particles that escape from the surface of the water get blown away. This means FEWER PARTICLES in the vapour will RETURN to the liquid. So, the rate of evaporation will increase.

What are the factors affecting evaporation?

Condensation is the opposite of evaporation — it is when a gas changes to a liquid. Condensation can warm up the surroundings as heat energy is transferred to it (latent heat of vaporization is released when water vapour condenses = thermal energy is released).

What is condensation?