Thermodynamics and Statistical Mechanics

A good question that nags many chemistry students simply because it is keenly ignored/avoided.

I guess that's because a decent explanation requires quantum mechanics...which I won't go into because it'd take a while to do it justice. But actually it's really simply stuff.

Anyhow, we can still get a good idea without any real quantum mechanics.

When you shine light at a molecule, the photons hit the electrons and excite them (energise them).

Essentially, molecules can absorb light but ONLY light at the absolutely correct energy (as it takes a specific energy to excite that electron and no more or less will work)...so now we can see molecules will only absorb certain energies of light...and thus, certain wavelengths...or certain colours - if you want to look at it that way.

So what happens to the light that isn't absorbed? It is scattered (reflected) and that's the light that hits our eyes and we see. What's interesting is that we see what is called the "complementary colour".

This is the colour that appears when you use all of the visible light spectrum EXCEPT the one absorbed. So if we absorb yellow light, we get everything else...which turns out to be blue when you mix it all up.

We kinda see the colour 'opposite' to that which is absorbed.

Worth noting, visible light is just a tiny part of the electromagnetic spectrum. You'll learn that so many compounds absorb U.V light. If we could see U.V with our eyes then many compounds that are colourless in the visible spectrum (like methane, a colourless gas) may well be visible to us.

And finally, you do tend to get strong colours from transition metal complexes. This is due to d-electron transitions...but if you need to know that you will be taught it specifically.

When nitrogen stored at 6000 psi is released into the atmosphere, it undergoes adiabatic expansion and experiences a drop in temperature due to the decrease in pressure. The final temperature will depend on various factors like initial temperature, volume, and surroundings.

This is a balanced chemical equation representing the reaction between nitrogen dioxide and oxygen gas to form nitrogen dioxide. The stoichiometry of the reaction shows that 2 moles of NO react with 1 mole of O2 to produce 2 moles of NO2.

No - compressed liquid is at a pressure above the boiling point pressure of the liquid. A saturated liquid is right at that boiling point. If you try to drop the pressure on a saturated liquid, it will begin to boil. If you start dropping the pressue on a compressed liquid, it will remail a stable liquid unit you have dropped it to the saturation pressure.

As temperature increases, the atoms will move around more energetically - moving on average faster. Translational speeds increase, rotational speeds of the molecules increase, and the magnitude of vibrations of the atoms about their bonds in molecules increase

As temperature decreases, the atoms move around less energetically - moving on average slower. Translational speeds decrease, rotational speeds of the molecules decrease, and the magnitude of vibrations of the atoms about their bonds in molecules decrease

In thermodynamics, a pure substance is a substance that has a constant chemical composition and uniform properties throughout. Examples include water, nitrogen, and oxygen. These substances can exist in multiple phases (solid, liquid, gas) and have characteristic phase change behavior under different conditions.

Heat radiates from your body in the form of infrared radiation, which can be felt by someone standing close to you. This is because your body is constantly generating heat as a result of metabolic processes, and some of this heat is transferred to the surrounding environment, including the person standing next to you.

Calculating absolute pressure with a U-tube manometer requires filling it with a non-volatile fluid and sealing one end. The non-sealed end is exposed to whatever fluid you wish to measure the pressure of. The difference in the height of the manometer fluid between the open arm and the sealed arm is an indication of absolute pressure. At zero absolute pressure the fluid should be at the same height in both arms with vacuum above the fluid in the sealed arm. From a practical standpoint, there are no fluids that have zero vapor pressure, but fluids are available with vapor pressures low enough to be negligible compared to the limitations of the ability of the person reading the measurements to read the height of the fluid. As an example, under most operating conditions mercury has a negligible vapor pressure. If you start getting up to high temperatures, however, all bets are off.

The fluid chosen for the manometer is somewhat dependent on what the fluid is that you wish to measure the pressure of - as well as cost. The cheapest fluid is probably water, but you have the obvious issue of evaporation. In the short term it works well thought because the water is cheap to replenish. It works particularly well when measuring pressure drops in pipes carrying hydrocarbons or oils in general because the water is pretty immiscible with the oil. Other common fluids are mineral oil and mercury because they have low vapor pressure.

Two reasons:

1. It almost impossible to pull a wire tight enough that it is straight.

2. The sag also can "give" a little if the wires shrink to to cold. If they could not "give" a little, then they would simply break.

An analogy for the laws of thermodynamics is the rules of a game. Just like how the rules of a game dictate what is and is not allowed during gameplay, the laws of thermodynamics govern how energy behaves in physical systems. They provide a framework for understanding and predicting energy interactions.

No, melting an ice cream scoop is an endothermic process because energy is absorbed to break the intermolecular bonds and change the solid ice cream into its liquid form.

No, exergy is a measure of a system's potential to do work and cannot be negative. If the exergy value calculated for a system results in a negative number, it is likely due to errors in the calculations or assumptions made.

Thermocouples can measure a wide range of temperatures however accuracy is a common limitation. Thermometers give consistent results however they may become decalibrated easily. Mercury thermometers are extremely accurate but they cannot be used at temperatures below negative 38 degrees Celsius.

The Zeroth Law of Thermodynamics states that if two systems are in thermal equilibrium with a third system, then they are in thermal equilibrium with each other. This law establishes the concept of temperature and allows for the definition of a common temperature scale.

isenthalpic expansion is through PRDS or control valve where entropy changes. Whereas expansion through a steam turbine is isentropic one and enthalpy drops. isentropic expansion is more efficient process as compared to isenthalic one.

Yes, a refrigerator is an example of a heat pump. It transfers heat from the interior of the fridge to the surroundings, thus cooling the interior. This process involves the compression and expansion of refrigerant to move heat energy.

The integral heat of solution can be determined experimentally by measuring the temperature change and volume change associated with the dissolution of a solute in a solvent. By using a calorimeter and conducting the experiment under controlled conditions, the heat of solution can be calculated by applying the principles of thermodynamics. This involves measuring the initial and final temperatures of the solution, and accounting for any heat absorbed or released during the process.

Priming occurs when a boiler has a high dissolved solids content which increases the surface tension of the water. Steam bubbles breaking through this surface tension often carry water over into the steam outlet of the boiler. Priming, also known as foaming, is what causes the carryover.

Most likely it's caused by the fact that supplied heat is transferred to external electronic orbits. When provided some energy external electrons will jump to higher levels which are located farther from nuclei then non-exited. The latter one causes effective radius of atom to increase, in its turn electronic levels of neighboring atoms get closer and in order for the system to be in equilibrium the atoms have to move from each other. As result bodies expend while is being heated.

Before starting a thermodynamic analysis, you should be familiar with the basic principles of thermodynamics, understand the properties of the system you are analyzing, and have a clear understanding of the boundary conditions and assumptions that apply to the specific problem you are studying. It's also important to have a good grasp of relevant equations and be able to apply them correctly to solve the problem at hand.

In adiabatic expansion, the velocity of a gas increases because the gas expands into a lower pressure environment, converting internal energy into kinetic energy. This increase in velocity is a result of the conservation of energy and the need to maintain equilibrium as the system adjusts to the changing conditions.

The glass transition temperature is the temperature at which an amorphous solid transitions from a rigid, glassy state to a rubbery state, without undergoing a distinct phase change. The melting point is the temperature at which a solid material transitions into a liquid state. The key difference is that the glass transition is a change in the physical properties of a material, while melting involves a change in its phase.

The moving air stream from a fan increases the rate of evaporation on the skin, which can make it feel cooler. The air movement also helps to dissipate body heat, making it feel cooler compared to still air.