When atoms and molecules speed up or slow down, that is a physical change. When they change state from liquid to solid or from gas to liquid, that is a physical change. ... The ions or molecules can still come back together to form the original substance
Answer:

Explanation:
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In this case, given the heat of fusion of THF to be 8.5 kJ/mol and freezing at -108.5 °C, for the required mass of 5.9 g, we can compute the entropy as:

Whereas n accounts for the moles which are computed below:

Thus, the entropy turns out:

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The given question is incomplete. The complete question is:What is the relative atomic mass of a hypothetical element that consists isotopes in the indicated natural abundances.
Isotope mass amu Relative abundance
1 77.9 14.4
2 81.9 14.3
3 85.9 71.3
Express your answer to three significant figures and include the appropriate units.
Answer: 84.2 amu
Explanation:
Mass of isotope 1 = 77.9
% abundance of isotope 1 = 14.4% = 
Mass of isotope 2 = 81.9
% abundance of isotope 2 = 14.3% = 
Mass of isotope 3 = 85.9
% abundance of isotope 2 = 71.3% = 
Formula used for average atomic mass of an element :

![A=\sum[(77.9\times 0.144)+(81.9\times 0.143)+(85.9\times 0.713)]](https://tex.z-dn.net/?f=A%3D%5Csum%5B%2877.9%5Ctimes%200.144%29%2B%2881.9%5Ctimes%200.143%29%2B%2885.9%5Ctimes%200.713%29%5D)

Therefore, the average atomic mass of a hypothetical element that consists isotopes in the indicated natural abundances is 84.2 amu
Answer : If we consider the molecule of oxygen gas which in diatomic state, is bonded to other atom which is of same element this is called as homonuclear.
While in HCl there is a heteronuclear bonding observed because there are two different elements getting involved in the bond formation, also it creates a electrovalent species in itself and makes it more polar. They are creating a dipole moment by separating different charges in the molecule which cause it to get tightly bonded with each other.
Answer:
18.33 ×10²³ atoms
Explanation:
Given data:
Molar mass of sulfuric acid = 98.1 g/mol
Mass of sulfuric acid = 75.0 g
Number of of oxygen atom present = ?
Solution:
Number of moles of sulfuric acid:
Number of moles = mass/molar mass
Number of moles = 75.0 g/ 98.1 g/mol
Number of moles =0.761 mol
one mole of sulfuric acid contain four mole of oxygen atom.
0.761 mol × 4 = 3.044 mol
1 mole = 6.022×10²³ atoms of oxygen
3.044 mol × 6.022×10²³ atoms of oxygen / 1mol
18.33 ×10²³ atoms