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Fiesta28 [93]
3 years ago
14

All elements in Group 18 are called________________ _______________ and are ______________, which means they don’t readily react

with other elements.
Chemistry
1 answer:
Arada [10]3 years ago
6 0

Answer:

All elements in Group 18 are called noble gases and are nonreactive which means they don’t readily react with other elements.

Explanation:

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Calculate the number of hydrogen atoms present in 40g of urea, (NH2)2CO
tekilochka [14]

Answer: There are 16.14 \times 10^{23} atoms of hydrogen are present in 40g of urea, (NH_{2})_{2}CO.

Explanation:

Given: Mass of urea = 40 g

Number of moles is the mass of substance divided by its molar mass.

First, moles of urea (molar mass = 60 g/mol) are calculated as follows.

Moles = \frac{mass}{molar mass}\\= \frac{40 g}{60 g/mol}\\= 0.67 mol

According to the mole concept, 1 mole of every substance contains 6.022 \times 10^{23} atoms.

So, the number of atoms present in 0.67 moles are as follows.

0.67 mol \times 6.022 \times 10^{23} atoms/mol\\= 4.035 \times 10^{23} atoms

In a molecule of urea there are 4 hydrogen atoms. Hence, number of hydrogen atoms present in 40 g of urea is as follows.

4 \times 4.035 \times 10^{23} atoms\\= 16.14 \times 10^{23} atoms

Thus, we can conclude that there are 16.14 \times 10^{23} atoms of hydrogen are present in 40g of urea, (NH_{2})_{2}CO.

7 0
3 years ago
Which statement correctly describes an atom of the element helium? (9)
Luden [163]

C. An atom of helium has its valence electrons in its first energy level, it wouldn't and can't satisfy the Octet rule as it only has 2 electrons, but with 2, it has a full shell, as the first energy level can hold only 2 electrons.

8 0
4 years ago
The temperature at which a solid melts is not characteristic if a compound nor an element
Assoli18 [71]

Answer:

False

Explanation:

The temperature at which a solid melts, known as its melting point is highly characteristic of a compound and element.

The melting point of pure substances, compounds and elements is definite and not varied.

  • Melting point is an intensive property of matter.
  • It does not depend on the amount of matter present.
  • It is an innate or intrinsic property of every matter.
  • For example, no matter the volume or mass of water, it will always boil at 100°C, all things being equal.

Therefore, melting point of most solids is characteristic of compounds and elements.

8 0
3 years ago
There are islands in the ocean that are growing larger. The Hawaiian Islands are good examples of this. The reason that the isla
Inessa [10]
My guess would be "B) they were produced by volcanoes" because hawaii has a bunch of volcanoes and volcanoes can produce extra land. While the other answers wouldn't make sense. Definitely B.
5 0
3 years ago
Which statements accurately describe osmosis?
Serhud [2]

Answer:

Osmosis is a type of passive transport. The best statement that accurately describes osmosis is: Osmosis is the diffusion of water across a membrane.

Explanation:

7 0
3 years ago
Read 2 more answers
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