Consider the following reaction:
Mg + 2H2O Mg(OH)2 + H2 ΔH = -353 kJ

This reaction is
A.
exothermic because heat is released.
B.
endothermic because heat is released.
C.
endothermic because heat is absorbed.
D.
exothermic because heat is absorbed.

Answer:

it because of cold weather

The process of grinding is a physical change that takes place in the mouth during digestion.

Grinding is one of the processes that occur during the digestion of food molecules into simpler substances.

Grinding of food molecules occurs in the mouth with the aid of the teeth, which is used to chew.

However, the process of grinding is a physical change because it does not result into the formation of new substances or change the chemical constituents of the food.

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Answer:

hydrogen and helium is the answer.

The line spectra of an atom offers conclusive evidence that electron energies are quantized.

Neils Bohr showed that electrons in an atom can absorb or emit energy when they move from one energy level to another. This principle is the basis upon which the spectra of atoms is built.

The true statements about the atomic spectra is;

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Answer:

2.4×1024 atoms.

Explanation:

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Answer: A.6

Explanation:

The total number of molecules in the chemical formula is 6

Molecules  are the smallest particle of a substance that has all of the physical and chemical properties of that substance. Molecules are made up of one or more atoms.

The correct form of question will be:-6 molecule of methane CH₄

                       6CH4

⇒ Number of aton of carbon is 6

⇒Number of atom of hydrogen is 24

⇒Total number of atom is 30

An atom is a particle of matter that neither be created nor be destroyed. An atom consists of a central nucleus that is usually surrounded by one or more electrons. Each electron is negatively charged. The nucleus is positively charged, and contains one or more relatively heavy particles known as protons and neutrons.

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Answer:

Ethanol is the odd one.....

Answer:

A = 55

Explanation:

The atomic number is the number of protons also = the number of electrons, so basically we have 29 neutrons, 26 electrons and 26 protons. Anyway, it's asking the mass number which is the neutrons + the protons, so you just take 29+26 = 55

Atomic number=26

Neutrons=29

Electrons=26

Mass number=Proton+neutron

Protons=26

Mass number=26+29

=55

1 mole of oxygen.

Answer:

solution given:

[tex]2Na+O_2=Na_2O_2\\2mole\:\: 1mole \:\: 1mole[/tex]

according to the above reaction,1 mole of oxygen is required to react with 2 moles of sodium to form sodium peroxide.

Explanation:

High conductivity of metals is caused by electrons that are free to move through the lattice.

hope this helps!

Answer:

the answers are given in the photo

Answer:

To identify a pure liquid substance using the physical properties of solubility, density, and boiling point. The physical properties of a pure substance can be measured without changing the composition of the substance.

Explanation:

Answer:

increase

Explanation:

Let's suppose we have a sample of air in a closed container. We heat the container and we want to predict what would happen to the pressure.

According to Gay-Lussac's law, the pressure of a gas is directly proportional to its absolute temperature.

Thus, if we increased the temperature of the air by heating it, its pressure would increase.

If a sample of air in a closed container was heated, the total pressure of the air would increase.

Answer:

Mechanical Waves

Answer:

The answer is designing an experiment

Explanation:

Since we already have a hypothesis, we need to test the hypothesis and this is done by designing an experiment that will do this test.

a.

The atomic radius of iridium is 1.355 Å

For a face-centered cubic unit cell, with edge length, a and atomic radius r,

we have a² + a² = (4r)²

2a² = 16r²

r² = a²/8

r = a/√8

Since a = 3.833 Å,

Substituting this into the equation, we have

r = a/√8

r = 3.833 Å/√8

r = 3.833 Å/2.828

r = 1.355 Å

So, the atomic radius of iridium is 1.355 Å

b.

The density of iridium metal is 22.67 g/cm³

To find the density of the iridium metal, we need to find the mass of atoms per unit cell.

So, for the face centered cubic iridium atom, there are 6 faces per unit cell × 1/2 atoms per face + 4 corners per unit cell × 1/4 atoms per corner = 3 atoms + 1 atom = 4 atoms per unit cell.

So, the mass of the atoms in the unit cell is m = number of atoms/cell × number of moles/atom × molar mass of Iridium

= 4 atoms/cell × 1 mol/6.022 × 10²³ atoms × 192.22 g/mol

= 768.88/6.022 × 10²³ g/cell

= 127.68 × 10⁻²³ g/cell

= 1.2768 × 10⁻²¹ g/cell

Next, we need to find the volume of the unit cell which is V = a³

= (3.833 Å)³

= (3.833 × 10⁻¹⁰ m)³

= 56.314 × 10⁻³⁰ m

= 5.6314 × 10⁻²⁹ m

So, the density of iridium = mass of unit cell/volume of unit cell

= m/V

= 1.2768 × 10⁻²¹ g/cell ÷ 5.6314 × 10⁻²⁹ m

= 0.2267 × 10⁸ g/m³

= 0.2267 × 10⁸ g/m³ × 10⁻⁶ m³/cm³

= 0.2267 × 10² g/cm³

= 22.67 g/cm³

So, the density of iridium metal is 22.67 g/cm³

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Answer:

10.C

11.B

15.A

Explanation:

Answer:

If a compound is made from a metal and a non-metal, its bonding will be ionic. If a compound is made from two non-metals, its bonding will be covalent.

Answer:

21% oxygen and 78%nitrogen

Explanation:

Answer:

Nitrogen and Oxygen

Explanation:

nitrogen - 78 %

oxygen - 21%

Explanation:

Electrons are closer to the nucleus are in filled orbitals and are called core electrons. More energy which in nucleus called nuclear strOng energy to remove electron thars why its also a way harder too..

Answer:

20g

Explanation:

hope helpful.............

Answer:

NaCI + H2O

this is answer

Answer:

2) To find the atoms from the moles, you just multiply Avogadro's number (6.02 x 10^23) by the moles.

So 3.35 x (6.02 x 10^23) = 2.0167 x 10^24 atoms are in 3.35 moles of aluminum

3) If the question is asking under standard temperature and pressure, we know that if we divide the volume by the molar volume of a gas (which is 22.7 in standard temperature and pressure), we can get the moles.  

So 101.25L / 22.7 = 4.46 mol

4) We know that to find the moles, it is the mass divided by the molar mass. If we rearrange the equation to solve for mass, we have to multiply the moles by the molar mass to get there.

Nitrogen's (N) molar mass on the periodic table is 14g/mol, but since Nitrogen is a diatomic element, it would be N2 by itself. So multiply 14 by 2, which will give you 28g/mol. N2's molar mass is 28g/mol.

Now you multiply 13.7 moles by 28g/mol, which will give you 383.6g

Just did a few edits here, 4.46 for question 3 is in moles not L

Taking into account the definition of avogadro's number,

2. 3.35 moles of aluminum contains 2.018ײ⁴ atoms.

3. 4.52 moles of CO₂ gas are in a 101.25 L container filled with CO₂ gas.

4. 13.7 moles of N₂ contain 383.6 grams.  

Avogadro's Number is called the number of particles that make up a substance (usually atoms or molecules) and that can be found in the amount of one mole of said substance. Its value is 6.023×10²³ particles per mole. Avogadro's number applies to any substance.

Then you can apply the following rule of three: if 1 mole of aluminum contains 6.023×10²³ atoms, then 3.35 moles of aluminum contains how many atoms?

amount of atoms of aluminum= (6.023×10²³ atoms × 3.35 moles)÷ 1 mole

amount of atoms of aluminum=2.018ײ⁴ atoms

Finally, 3.35 moles of aluminum contains 2.018ײ⁴ atoms.

The STP conditions refer to the standard temperature and pressure. Pressure values at 1 atmosphere and temperature at 0 ° C are used and are reference values for gases. And in these conditions 1 mole of any gas occupies an approximate volume of 22.4 liters.

Then, you can apply the following rule of three: If by definition of the STP conditions 1 mole of CO₂ occupies a volume of 22.4 L, how many moles does 101.25 L occupy?

[tex]amount of moles of CO_{2} =\frac{101.25 Lx1 mole of CO_{2} }{22.4 L}[/tex]

amount of moles of CO₂= 4.52 moles

4.52 moles of CO₂ gas are in a 101.25 L container filled with CO₂ gas.

The molar mass of substance is a property defined as its mass per unit quantity of substance, in other words, molar mass is the amount of mass that a substance contains in one mole.

In this case, the molar mass of N₂ is 28 g/mole. So, you can apply the following rule of three:  If 1 mole of N₂ contains 28 grams, 13.7 moles of N₂ contain how much mass?

[tex]mass=\frac{13.7 moles x28 grams}{1 mole}[/tex]

mass= 383.6 grams

13.7 moles of N₂ contain 383.6 grams.

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Explanation:

Because of the earth and climate change the point of incidence mean that you mean by engineers to social evils activities.

Answer:

Word equation: Potassium chlorate → Potassium chloride + Oxygen

Chemical equation: KClO₃ → KCl + O₂

Explanation:

This is decomposition reaction so there will only be one reactant, which is potassium chlorate.

The chemical equation will be:

KClO₃ → KCl + O₂

The balanced equation would be:

2KClO₃ → 2KCl + 3O₂

The word equation will be:

Potassium chlorate → Potassium chloride + Oxygen