37 votes

How do you know mercury changes monotonically with temperature if mercury itself is used to make the thermometer?

Monotony just means that hotter always means bigger, unlike water that shrinks as you heat it from 0 °C to 4 °C. Above 4 °C it expands again. This means that about 2 °C and about 5 °C will give the ...
Stig Hemmer's user avatar
31 votes
Accepted

How do you know mercury changes monotonically with temperature if mercury itself is used to make the thermometer?

This has actually been a very important problem in the history of measurement and physics more broadly. The solution was an iterative process of increasing internal consistency and precision of ...
Martin Modrák's user avatar
29 votes
Accepted

How do batteries lose capacity in winter?

It is true that battery performance is reduced at colder temperatures. This is because temperature has an effect on chemical processes within the batteries, especially lithium-ion batteries, used most ...
joseph h's user avatar
  • 29.4k
22 votes

Do we understand chemistry from particle physics?

While the discoveries of the rules of chemistry and some current practical wisdom is empirical, it is better to think of the entire nature of chemistry as dictated by the principles of quantum ...
Matt Hanson's user avatar
  • 3,092
21 votes

How do batteries lose capacity in winter?

A deeper, physics/chemistry approach to the question: A battery (whatever chemistry it uses) invariably contains solid electrodes and liquid electrolyte (there are batteries that have it the other way ...
fraxinus's user avatar
  • 7,906
16 votes

How do you know mercury changes monotonically with temperature if mercury itself is used to make the thermometer?

You do not know it a priori, you assume it to be true and if it leads to contradiction with other experiments and theories based on all prior experiments then you have to investigate the source of ...
hyportnex's user avatar
  • 19k
13 votes

How do you know mercury changes monotonically with temperature if mercury itself is used to make the thermometer?

If you have no better theory of what temperature is, you define it as what your thermometer measures. That allows you to get started. Now, you can do experiments in thermal physics. If you don't see ...
John Doty's user avatar
  • 21k
12 votes

Can a broken chemical bond be made again?

This is exactly what chemical equilibrium teaches. Take a reaction, for example $$ 2\text{NH}_3 \leftrightharpoons \text{N}_2 + 3\text{H}_2 $$ which is endothermic. Increasing $T$ moves the ...
Themis's user avatar
  • 5,861
11 votes
Accepted

Do particles (e.g. atoms/electrons) in large molecules that rotate experience pseudoforces?

If you were to analyze the molecular vibrations and rotations rigorously correctly, you would end up with Coriolis coupling constants between the vibrations and rotations that arise due to the ...
Matt Hanson's user avatar
  • 3,092
11 votes

Do we understand chemistry from particle physics?

atoms have 8 electron "slots" in their outer shell The shape of the periodic table is one of the great successes of non-relativistic quantum mechanics. If we approximate that we're ...
rob's user avatar
  • 89.9k
10 votes
Accepted

Why cookies don't soak linearly in function of temperature?

A cookie is roughly starch granules held together by sugar and sometimes fat. At higher temperatures this matrix dissolves faster, and this makes it fall apart quickly. However, at higher temperature ...
Anders Sandberg's user avatar
9 votes

How do batteries lose capacity in winter?

In addition to the charge in the battery itself, you also need to consider increased HVAC usage. Unlike an internal combustion engine vehicle, which produces waste heat as a byproduct of combustion ...
StalePhish's user avatar
9 votes

Can a broken chemical bond be made again?

It is certainly possible. If you heat water so that it boils into steam then you are basically supplying enough thermal energy to break the hydrogen bonds that exist between water molecules in the ...
gandalf61's user avatar
  • 53.6k
9 votes

An egg gets soft before it gets hard

The white of an egg is a complicated mix of water and proteins. The viscosity of such a mixture as a function of temperature is almost impossible to predict but in general it will go down as the ...
niels nielsen's user avatar
9 votes

Why is the mole an SI unit?

The SI is not comprised of the minimal possible number of fundamental dimensional constants. In fact, it is chosen to be fairly redundant, which tends to be somewhat useful for experimental practice. ...
Níckolas Alves's user avatar
8 votes

An egg gets soft before it gets hard

The viscosity of homogenized liquid egg is reported in, for example, Bozkurt and Icier's "The change of apparent viscosity of liquid whole egg during Ohmic and conventional heating," J Food ...
Chemomechanics's user avatar
8 votes

Why is the mole an SI unit?

Chemists measure quantities of material in moles because the progress and outcomes of a chemical reaction may depend on having a well-understood stoichiometry among the constituents. If you want to ...
rob's user avatar
  • 89.9k
6 votes
Accepted

Why do dry lentils cluster around air bubbles?

when a dry lentil first encounters water, the water initially does not wet the surface of the lentil well- that is, the lentil is happier in contact with air rather than with water. This means if ...
niels nielsen's user avatar
6 votes

Why is the mole an SI unit?

In fact, pretty much every unit of measure can be expressed as other units if we wish. Temperature can easily be expressed as average energy. In the original CGS system of electrical units, the unit ...
RC_23's user avatar
  • 9,121
6 votes

Koopman's Theorem for Ionization energy and electron affinity

I will present a more quantitative version of the (mostly verbal) argument given at the end of Sec. 3.3.1 in Modern Quantum Chemistry by Szabo & Ostlund. The argument goes like this. Let us first ...
dennismoore94's user avatar
6 votes

Do we understand chemistry from particle physics?

"Do we understand chemistry from particle physics?" I suggest that the answer is 'no', but some people believe on a theoretical basis that we should be able to understand chemistry from ...
terry-s's user avatar
  • 296
5 votes

Why chemists usually only deal with enthalpy and not internal energy?

The internal energy is a thermodynamic potential, that gives the intrinsic energy content of a system at equilibrium with a given particle number, entropy and volume: $$ U(S, V, N) $$ Enthalpy on the ...
Sebastian Riese's user avatar
5 votes

How do batteries lose capacity in winter?

The charge in a rechargeable battery is literally a charge, i.e. a quantity of electrons that have been moved. Charge is conserved; temperature change does not alter it. It is normal to stop adding ...
Whit3rd's user avatar
  • 9,758
5 votes

Do particles (e.g. atoms/electrons) in large molecules that rotate experience pseudoforces?

In classical physics, there are not really any "properties that arise because of these pseudoforces". How can there be when we always have the option of working in an inertial frame? A ...
Connor Behan's user avatar
  • 7,266
5 votes
Accepted

Conservation of water?

The number of water molecules is certainly not constant, because chemical reactions can create or destroy water. A simple example is metabolism of Glucose, which creates water. $C_6H_{12}O_6 + 6O_2 \...
Allure's user avatar
  • 20.6k
5 votes

General Doubt. My doubt about combustion

Boiling water is not hot enough to ignite the paper. If you were to pour molten metal on the paper instead then it would burn. Note that the source of oxygen is from the surrounding air - the fact ...
gandalf61's user avatar
  • 53.6k
4 votes

Bubbles formed in standing water in glass

It is more like bubbles coming out of fizzy water than boiling. Water often has air dissolved in it. If you let it sit, it can come out of solution. This happens at the surface, where the water ...
mmesser314's user avatar
  • 38.7k
4 votes

Is Hartree-Fock (HF) a ground state theory?

From a practical point of view, HF is (almost) always used for ground state calculations, as was nicely explained by Hans Wurst. However, within certain limits, HF calculations can be performed for ...
dennismoore94's user avatar
4 votes

Chemical Potential and Gibbs Energy

Starting from $U=TS-pV+\sum \mu_j N_j$ it is true that when you define the Gibbs potential as $G=U-TS+pV$ then $$G=\sum \mu_j N_j \tag{1}$$ and also $$dG = dU-TdS-SdT+pdV+Vdp=\sum \mu_j dN_j+\sum N_j ...
hyportnex's user avatar
  • 19k
4 votes
Accepted

The relation between state function and molecular orbitals

Molecular orbitals are simply used to construct $N$-electron basis states (Slater determinants). First, let us have a one-particle Hilbert space $\cal{H}$ of dimension $M$, with $M$ linearly ...
dennismoore94's user avatar

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