THERMODYNAMICS

Thermodynamics Thermodynamics is the study of heat. Kinetic-Molecular Theory - matter is made up of tiny particles in motion. In hot objects (high energy) the particles move faster, and in cold objects (low energy) they move more slowly.

Thermal Energy versus Temperature Thermal Energy is the overall energy of motion of all particles making up the object. Thermal energy depends on the number of particles in the object. Twice the mass gives twice the thermal energy. Temperature is the “hotness” of the object. Temperature does NOT depend on the number of particles in a body. It depends on the average kinetic energy of the particles. Twice the mass gives the same temperature.

Temperature Scales Farenheit and celciusCelcius and Kelvin Temperature is a measure of an object’s “hotness”. Absolute zero is the temperature where all molecular motion stops. All thermal energy is removed. F = (C X (9/5)) + 32

Temperature Scales

Practice Convert 250 K to C : use C = K – 273 Convert 50 C to F: use F = (C x (9/5)) +32 Convert 42 F to K: use C = 5/9(F – 32) and K = C + 273

So does Heat do Work? YES!! The transfer of energy in the form of heat is associated with –changes in the temperature or –changes in the state of a sample of matter. Energy transfer in the form of heat can result in the performance of work upon the system or the surroundings.

THERMAL ENERGY & MATTER Work and Heat- work is never 100% efficient. Some is always lost to heat.

Heat- the transfer of thermal energy from one object to another because of a temperature difference. In what direction does heat flow spontaneously? FROM HOT to COLD

Heat flows DOWN the bar through COLLISIONS. Collisions transfer thermal energy from hot to cold.

Thermal energy- total potential and kinetic energy in an object. It depends on mass, temperature, and phase of an object. If both objects are in the same phase & at the same temperature, which one has MORE thermal energy?  Because there are MORE particles moving around.

Let’s look at phase changes… The phase of matter depends upon it’s temperature and the pressure exerted upon it. Changing phase usually involves a transfer of energy.

Liquid to Gas Liquid changing to gas at the surface is called evaporation. Evaporation is a endothermic process. Endothermic – energy added to the system.

Liquid to Gas Liquid changing to gas below the surface is called boiling. Boiling depends on both temperature AND pressure! Boiling is a endothermic process.

Gas to Liquid Condensation is the opposite of evaporation. Condensation is a exothermic process. Exothermic – energy is released from the system.

Liquid to Solid Change in phase from liquid to solid is called freezing. Like boiling, freezing is affected by pressure. This is known as a exothermic process.

Solid to Liquid Change in phase from solid to liquid is called melting. Melting point is the same as freezing point. Endothermic process

Skipping the Liquid Phase At some temperatures and pressures, materials may go directly from solid to gas (sublimation) - endothermic process or from gas to solid (deposition)- exothermic process Some materials experience these phenomena under normal conditions. – carbon dioxide (dry ice) and naphthalene (moth balls) are example of sublimation. - Frost and snowflakes are examples of deposition of water molecules.

Energy and Phase Change The amount of energy required to change the state of matter depends on three things: 1.What the substance is… 2.How much of the substance is undergoing the state change 3.What state of change that is occurring

THERMAL ENERGY & MATTER Thermal expansion/contraction - change in volume of a material due to temperature change. Occurs because particles of matter collide more or less as temperature changes. Thermal expansion  

Specific Heat – amount of heat needed to raise ONE gram of a material ONE degree Celsius.

The LOWER a material’s specific heat the MORE it’s temperature rises when energy is added. Which will heat faster? Water? Or Lead? YES! Specific heat of water = 4.18 J/g°C Specific heat of lead = 0.46J/g°C

Conductors: Good vs. Bad Low specific heat = good thermal conductors High specific heat = bad thermal conductors

Specific Heat

Q(heat) = J M(mass) = kg C(specific heat) = J/(kg∙K) T(temperature) = K

Example A 1.63-kg cast-iron skillet is heated on the stove from 295 K to 373 K. How much heat had to be transferred to the iron? m = 1.63 kgQ = C p ΔTm ΔT = 78 K C p = 450 J/kgK Q = 57,213 J

Specific Heat Measurement Calorimeter - A well insulated device used to measure changes in thermal energy.

HEAT TRANSFER What type of HEAT TRANSFER is occurring in the pictures? Conduction, convection or radiation? CONDUCTION – The transfer of thermal energy with no transfer of matter.

Conduction Two bodies are physically touching. The molecules in one can collide with the molecules in the other. The collisions can cause an exchange of energy

HEAT TRANSFER What type of HEAT TRANSFER is occurring in the pictures? Conduction, convection or radiation? CONVECTION – The transfer of thermal energy when particles of a liquid or gas move from one place to another

Convection Carried hot cup of coffee across the room. Hot smoke from a fire rises up into the sky. Heat is carried upwards.

HEAT TRANSFER What type of HEAT TRANSFER is occurring in the pictures? Conduction, convection or radiation? RADIATION – The transfer of thermal energy by waves moving through space. ALL OBJECTS radiate energy!

Radiation Light is electromagnetic waves or electromagnetic radiation. “Radiation” is “light”. And light contains energy.

All objects emit light Everything, everywhere, all the time emits light. Very hot objects will emit visible light (like light bulbs, the Sun, or flames). Cooler objects emit light as well, usually infrared radiation that our eyes don’t detect.

Different types of light radio, microwave, infrared, visible, ultraviolet, X-ray, gamma ray

Light and Energy Light waves carry energy. Radio and microwave are low-energy light. Infrared and visible are medium-energy. Ultraviolet, X-ray, Gamma ray are high energy. Emitting light is losing energy. Absorbing light is gaining energy.

Emission and Absorption Everything emits radiation (light) continuously. Human bodies, walls, stars, trees, pencils,… Everything absorbs light continuously. There can be a net gain or loss of energy (heat) depending on the difference between the total energy it emits or absorbs.

Radiation Emission Hotter objects emit more radiation than otherwise identical objects that are cooler. Larger objects emit more radiation than otherwise identical objects that are smaller. Emission also depends on the object’s color. RqGs

THERMODYNAMICS The study of conversions between thermal energy and other forms of energy.

The four laws of Thermodynamics The 0 th Law (discovered 4 th ) The 1 st Law (discovered 2 nd ) The 2 nd Law (discovered 1 st ) The 3 rd Law (discovered 3 rd )

The 0 th Law If: – Objects A and B are the same temperature – Objects B and C are the same temperature Then: – Objects A and C are the same temperature – Just the transitive property of mathematics.

THERMODYNAMICS First Law: Energy is Conserved This is a restatement of the Law of Conservation of Energy: Energy is neither created nor destroyed but can change form.

Laws of Thermodynamics The first law of thermodynamics is “Whenever heat flows into or out of a system, the gain or loss of thermal energy equals the amount of heat transferred.” The first law is also known by another name: conservation of energy.

Second Law of Thermodynamics The Second Law of Thermodynamics states that natural processes go in a direction that maintains or increases the total entropy of the universe. Things tend to become more and more disordered. So moves hot to cold. Food color drops added to a glass of water demonstrates diffusion and the second law of thermodynamics. Entropy is a measure of the disorder of a system.

Entropy is a measure of how evenly spread out the energy is. Entropy is a measure of energy that is no longer “useful,” or “workable.” Work is change in energy. It won’t change anymore if it’s spread out evenly. (Work won’t change anymore if the temperature is spread out evenly.)

Examples of entropy Entropy is randomness. Which is more random? A or B? AB

Examples of entropy 2 nd Law of Therm. says that nature always goes from order to disorder. AB

More examples of entropy

On the large scale, the ice “looks” more disordered. On the small scale, the solid phase severely limits where the molecules could be. The ice crystal molecules are much more ordered than the free moving liquid water molecules.

3 rd law of Thermodynamics “Absolute zero” is a state of zero motion. – This means absolutely no entropy. – So it can’t be reached.