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stira [4]
3 years ago
7

Are blue stars young or old? How can you tell?.

Chemistry
1 answer:
andriy [413]3 years ago
4 0
Astronomers measure the brightness of stars using light-years. This means that the light we see now left in that years ago, traveling through space in that distance at kilometer per second.

A star is born, it radiates energy for a long time, toward the end it expands, it may or may not explode, and then it dies. It vary in sizes, masses and surface temperature range. The colors of stars reflect their surface temperature. Their relative brightness is expressed in a scale of six magnitudes. The brightest the stars are first-magnitude stars, while the dimmest are sixth-magnitude stars.
 
The lower the number, the brighter the star.

For example:
                      Star color                        Surface Temperature
                     Blue-white                         around 25 000 K & higher
                     white                                  around 10 000 K
                     yellow                                around 7 000 K
                     Red                                    around 5 000 K & lower

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Arrange the following alkyl bromides in order from most reactive to least reactive in an SN2 reaction: 1-bromo-2-methylbutane, 1
xxMikexx [17]
Primary alkyl halides tend to undergo the SN2 reaction mechanism in nucleophilic substitution since there is less steric hindrance for nucleophilic attack and the carbocations that they form are not as stable as those formed from tertiary alkyl halides. 


1-bromopentane > 1-bromo 2-methylbutane > <span>1-bromo-3-methylbutane</span>> 2-bromo 2-methylbutane
5 0
3 years ago
Read 2 more answers
luminum and oxygen react according to the following equation: 4Al(s) +3O2(g) --&gt; 2Al2O3(s) What mass of Al2O3, in grams, can
Slav-nsk [51]

Answer: 8.7 grams

Explanation:

According to avogadro's law, 1 mole of every substance occupies 22.4 L at STP and contains avogadro's number 6.023\times 10^{23} of particles.  

To calculate the moles, we use the equation:

\text{Number of moles}=\frac{\text{Given mass}}{\text {Molar mass}}=\frac{4.6g}{27g/mol}=0.17moles

4Al(s)+3O_2(g)\rightarrow 2Al_2O_3(s)

As oxygen is in excess, Aluminium is the limiting reagent and limits the formation of products.

According to stoichiometry:

4 moles of aluminium give = 2 moles of Al_2O_3(s)

Thus 0.17 moles of aluminium give=\frac{2}{4}\times 0.17=0.085mol

Mass of Al_2O_3=moles\times {\text {molar mass}}=0.085\times 102g/mol=8.7g

Thus the mass of Al_2O_3(s)  is 8.7 grams

8 0
3 years ago
Why do molecular compounds have low melting points and low boiling points relative to ionic substances?​
kap26 [50]

Answer:

The melting and boiling points of molecular compounds are generally quite low compared to those of ionic compounds. This is because the energy required to disrupt the intermolecular forces between molecules is far less than the energy required to break the ionic bonds in a crystalline ionic compound

4 0
3 years ago
Which pair of elements would most likely combine to form a salt? I and F Cs and I Na and C N and F
Savatey [412]

Answer:

Cs and I

Explanation:

Salts are formed when an ionic bond is formed between two elements in the compound. Let us recall that the kind of bond formed between any two elements depends on the magnitude of electronegativity difference between the two elements.

Among the options listed, the highest degree of electronegativity difference occurs for the bond between Cs and I. This implies that this bond is ionic and the combination of the two elements will lead to salt formation.

7 0
3 years ago
What does a fluorine ion have in common with a neon and a sodium ion
DanielleElmas [232]
The atomic number (Z) of the 3 elements F, Ne, and Na, are 9, 10, and 11.

Explanation:

Now Z refers to the number of protons in the element's nucleus, and protons are POSITIVELY charged particles. So a fluoride ion, F−, has 10 electrons rather than 9 (why?), a neutral neon atom has 10 electrons, and a sodium ion, Na+, also has 10 electrons (why?).

So the 3 species are ISOELECTRONIC; they possess the same number of electrons. 

You should look at the Periodic Table to confirm the electron number. Elements are (usually) electrically neutral (sometimes they can be ionic if they have lost or gained electrons). If there are 10 positively charged protons in the nucleus, there are NECESSARILY 10 electrons associated with the NEUTRAL atom. I don't know WHY I am capitalizing certain WORDS.

You might ask why sodium will form a positive ion, Na+, whereas F forms a negative ion, F−. This again is a Periodic phenomenon, and explicable on the basis of the electronic structure that the Table formalizes.

Neutral metals tend to be electron-rich species, which have 1 or more electrons in a valence shell remote from the nuclear charge. On the other hand, neutral non-metals have valence electrons in incomplete shells, that do not effectively shield the nuclear charge. The demonstrable consequence is that metals lose electrons to form positive ions, whereas non-metals gain electrons to form negative ions.

6 0
3 years ago
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