The universe is mostly made up of what?

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Answer 1

Answer: the universe is made mostly of empty space nothing else even close.

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Calculate the mass of 139 cm^3 Argon at STP

How does Bohr’s model of the atom compare with Thomson’s model?

Answers

J.J.Thompson discovered that cathode rays are negatively charged particles. According to J.J.Thompson’s plum pudding model, electrons are negative charges that embedded in a sea of positive charge like a pudding. According to Bohr’s atomic model electrons are found in discrete orbits around the nucleus. Bohr proposed that the electrons have quantized energy hence they do not spin and fall into nucleus thus making an atom highly stable.

Bohr's model of the atom states that electrons orbit an atom's nucleus in electron shells of increasing energy. The electrons are free of physical contact with the nucleus, but are held in orbit due to the electrons' attraction to the oppositely charged protons in the nucleus.
Thomson's model, or the plum pudding model, it describes atoms as spheres of positively charged matter, in which electrons are embedded in.
The key difference is the locations of, and the motions of the electrons.

What property of an atom determines its general reactivity?

Answers

The Chemical reactivity of metals varies with your eletropositividade, so the more eletropositivo is the most reactive element is metal. The most reactive metals are those that have great tendency to lose electrons and therefore form positive ions with more ease.

hope this helps!

at standard pressure how do the boiling point and the freezing point of NaCl compare to the boiling point and freezing point of H2O

Answers

Usually in this context you would be referring to the boiling and freezing point of a NaCl solution (saltwater) compared to pure H_{2}O. Sematics would be different for NaCl compound itself, you would say melting and boiling point for a solid substance- and the temperatures would be very, very radical (high).
The boiling point of pure water is 100 degrees C (212 F), and the freezing/melting point is below 0 degrees C (32 F). For a salt water solution, the boiling point is raised and the melting point is lowered. This means that water will stay liquid for an increased range of temperature. Depending on the amount of NaCl solute in the water, the boiling and melting points may change a few degrees.

Which equation represents sublimation?(1) I2(s) ==> I2(g) (3) I2(l)==>I2(g)
(2) I2(s) ==>I2(l) (4) I2(l)==>I2(s)

Answers

Answer : The correct options is, (1) $I_2(s)\rightarrow I_2(g)$

Explanation:

(1) $I_2(s)\rightarrow I_2(g)$ :

This reaction shows sublimation process in which the phase changes from solid state to gaseous state at constant temperature.

(2) $I_2(l)\rightarrow I_2(g)$ :

This reaction shows evaporation process in which the phase changes from liquid state to gaseous state at constant temperature.

(3) $I_2(s)\rightarrow I_2(l)$ :

This reaction shows melting process in which the phase changes from solid state to liquid state at constant temperature.

(4) $I_2(l)\rightarrow I_2(s)$ :

This reaction shows freezing process in which the phase changes from liquid state to solid state at constant temperature.

Hence, from this we conclude that the option (1) equation represents sublimation process.

The answer is (1). The definition of sublimation is the change of solid substance directly to gas. In the equation, the "s" stands for solid. The "l" stands for liquid. And the "g" stands for gas.

Which compound has the lowest vapor pressure at 50°C?(1) ethanoic acid (3) propanone
(2) ethanol (4) water

Answers

The compound that has the lowest vapor pressure is ethanoicacid. The correct option is 1.

What is vapor pressure?

Vapor pressure is a measure of a material'stendency to change into a gaseous or vapor state, and it rises with temperature.

The boilingpoint of a liquid is the temperature at which the vapor pressure at its surface equals the pressure exerted by its surroundings.

A liquid with weak intermolecularforces evaporates faster and has a higher vapor pressure. A liquid with stronger intermolecular forces is more difficult to evaporate and thus has a lower vapor pressure.

At 50°C, ethanoloicacid has the lowest vapor pressure, which is 0.08 atm. Propanone has a vapor pressure of 0.84 atm at 50°C. At 50°C, ethanol has a vapor pressure of 0.30 atm.

Thus, the correct option is 1.

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Answer : Option A) Ethanoic Acid

Explanation : Ethanoic acid has the lowest vapor pressure i.e 0.08 atm at the temperature of 50°C compared to the other given options.

The vapour pressure of propanone at 50°C is 0.84 atm

Ethanol has vapour pressure as 0.30 atm at 50°C

water has vapour pressure of 0.12 atm at 50°C.

Which pure substance can be classified as an element?
-H2
-NO3
-NaCl
-H2SO4

Answers

An element is made up of only one kind of atom.
So H2 is the element. Why? because H2 is made up of only one kind of atom, hydrogen atoms.

- Just as a side note, compounds (made up of atoms from more than one element) are also considered pure substances.

Answer: H2

Explanation: i took the quizz

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