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Answer:

Average atomic mass = 19.9 amu

Explanation:

Isotopes can be defined as two or more forms of a chemical element that are made up of equal numbers of protons and electrons but different numbers of neutrons.

Generally, the isotopes of a chemical element have the same chemical properties because of their atomic number but different physical properties due to their atomic weight (mass number).

Given the following data;

Relative abundance of Z-19 = 55%

Relative abundance of Z-21 = 45%

Atomic mass of Z-19 = 19 amu

Atomic mass of Z-21 = 21 amu

To find the average atomic mass;

Average atomic mass = 19 * (55/100) + 21 * (45/100)

Average atomic mass = 19*0.55 + 21*0.45

Average atomic mass = 10.45 + 9.45

Average atomic mass = 19.9 amu

Therefore, the average atomic mass for element Z is 19.9 amu.

Answer: D) 2.41 m

Explanation:

Molality of a solution is defined as the number of moles of solute dissolved per kg of the solvent.

where,

n = moles of solute

  = weight of solvent in kg

moles of solute =

volume of solution = 1L = 1000 ml      (1L=1000ml)

Mass of solution=

mass of solute = 292 g

mass of solvent = mass of solution - mass of solute = (1108- 292) g = 816g = 0.816 kg

Now put all the given values in the formula of molality, we get

Therefore, the molality of solution will be 2.41 mole/kg

Final answer:

In this problem, we calculate molality by using the given mass of the solute, the mass of the solvent, and the molar mass of the solute. After performing the necessary calculations, we find that the molality is 2.41 m.

Explanation:

The subject of this student's question is molality, which is a measure of the concentration of a solute in a solution. It is defined as the number of moles of solute per kilogram of solvent. To find the molality (m), we need to know the mass of the solute and the mass of the solvent in the solution.

Given, that the solution contains 292g of Mg(NO3)2 per liter (which is the mass of the solute). The density of the solution is 1.108g/mL. We know that 1L = 1000mL, so the mass of the solution is density x volume = 1.108g/mL x 1000mL = 1108g.

We need to find the mass of the solvent (water). The mass of the solution is the mass of the solute + the mass of the solvent. So, the mass of the solvent is 1108g(mass of the solution) - 292g(mass of solute) = 816g or 0.816gkg.

The molar mass of Mg(NO3)2 is 148.31452 g/mol. So, the number of moles of Mg(NO3)2 in the solution is moles = mass / molar mass = 292g / 148.31452 g/mol = 1.97 moles.

Now we can calculate molality (m) = moles of solute/mass of solvent in kg = 1.97 moles / 0.816 kg = 2.41 m. Therefore, the answer is D) 2.41 m.

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Answer:

d. Ar, because of its higher effective nuclear charge

For the secon part see explanation below.

Explanation:

The first ionization energy is the energy required to remove an electron from the atom from its outermost shell. It depends on the nuclear charge, distance from the nucleus and the screening of other electrons in the inner shells of the atom.

Comparing Cl and Ar we see that being both elements of the third period, the Ar atom has one more proton than Cl and therefore the electron feels more nuclear charge making the first ionization of Ar greater than Cl.

a) False, electronegativity relates to attraction for an electron and not to the first ionization.

b) False, again electron affinity is not first ionization, it is defined as the energy released when the atom captures an added electron.

c) False,athough it is true that Ar has  a complete octet, the higher first ionization is affected by nuclear charge. The screening of electrons in the n= 1 and 2 shells is almost the same so what is important is that the electrons in the n= 3 shell feel more nuclear charge.

d) True for all the reasons given previously : the higher effective nuclear charge in Ar.

For the second part, we have to make an inventory of the bonds being broken and formed:

ΔHºrxn = H broken - H formed, where H is the bond energy

H2 C = CH_2  +   H-Br    ⇒   CH_3CH_2Br

ΔHºrxn  = ( 1 C=C + 4 C-H + 1 H-Br)   -   ( 1 C-C + 5 C-H + 1 C-Br)

ΔHºrxn (kJ) =  (614 + 4(413) + 363) - ( 347 + 5 (413) + 276)

ΔHºrxn (kJ) = 2629 -  2688 =  -59 kJ

This value is not in the choices due to mistaken bond energy values from the tables.

Answer:

1. Ar, because of its higher effective nuclear charge.

2. ∆Hrxn = -200 KJ/mol

Explanation:

The size of the atoms of chemical elements can be measured from their atomic radius which is also affected by the effective nuclear charge.

Recall that elements in a particular period have the same number of electron shells. Also, along a given period, atomic radius decreases due to an increase in the effective (positive) nuclear charge. This is because as the atomic (proton) number increases along that period, the charge on the nucleus also increases. With more protons in the nucleus the overall attraction between the positively charged nucleus and the negatively charged surrounding electrons increases, so the electrons are pulled closer to the nucleus thereby leading to a decrease in the atomic size.

So, along a given period atomic size decreases due to an increase in the effective nuclear charge.

The first ionization energy is the minimum energy (in kilojoules) needed to strip one mole of electrons from one mole of a gaseous atom of an element to form one mole of a gaseous unipositive ion.

Along a particular period, ionization energy increases due to an increase in the effective nuclear charge and a decrease in atomic radius. This is because, the smaller the atom the more stable it is and the more difficult it will be to remove an electron.

For the second question,

The enthalpy change of a reaction is the difference in the bond dissociation energies of the reactants and products. Bonds are broken in reactant molecules and formed in product molecules. Bond breaking energies are usually intrinsic ( endothermic, +be ∆H ) while bond forming energies are usually extrinsic ( exothermic, -ve ∆H ).

So,

∆Hrxn = n∆H(reactants/bonds broken) - m∆H(products/bonds formed)

Where n and m = stoichiometric coefficients of the products and reactants respectively from the balanced chemical equation.

First, draw the correct Lewis structures of the compounds.

Next, identify all the bonds broken and formed.

Then, from the bond dissociation energies ( usually given or looked up in texts ), sum up the bond breaking energies and the bond forming energies and subtract the bond forming energies from the bond breaking energies.

Considering this equation:

H_2C = CH_2 + H-Br rightarrow CH_3CH_2Br

The equation is balanced.

Bonds broken (number of bonds ):

I. C=C (1)

II. H-Br (1)

III. C-H (4)

Bonds formed:

I. C-C (1)

II. C-H (5)

III. C-Br (1)

∆Hrxn = [ ( 1 x C=C ) + ( 4 x C-H ) + ( 1 x H-Br ) ] – [ ( 1 x C-C ) + ( 5 x C-H ) + ( 1 x C-Br ) ]

∆Hrxn = [ ( 1 x 614 ) + ( 4 x 413 ) + ( 1 x 141 ) ] – [ ( 1 x 348 ) + ( 5x 413 ) + ( 1 x 194 ) ]

∆Hrxn = [ ( 614+1652+141) ] – [ ( 348 + 2065 + 194 ) ]

∆Hrxn = 2407 – 2607

∆Hrxn = -200KJ/mol

Answer:

B) pH = 3.67

Explanation:

Taking into account the Charles's law, the same amount of gas at the same pressure and 55 ∘C would occupy a volume of 26.91 L.

Charles's Law consists of the relationship that exists between the volume and the temperature of a certain quantity of ideal gas, which is maintained at a constant pressure.

This law states that the volume is directly proportional to the temperature of the gas: if the temperature increases, the volume of the gas increases, while if the temperature of the gas decreases, the volume decreases.

Mathematically, Charles's law is a law that says that when the amount of gas and pressure are kept constant, the quotient that exists between the volume and the temperature will always have the same value:

Studying an initial state 1 and a final state 2, it is satisfied:

In this case, you know:

• V1= 22.4 L
• T1= 0 C= 273 K
• V2= ?
• T2= 55 C= 328 K

Replacing:

Solving:

V2= 26.91 L

Finally, the same amount of gas at the same pressure and 55 ∘C would occupy a volume of 26.91 L.

Learn more:

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Answer:26.9L

Explanation: this is Charles' law which states that the volume of a gas is directly proportional to the absolute temperature at contant pressure. The expression is V1/T1 = V2/T2

Making V2 the subject of the formula we have

V2 = V1 xT2/T1

= 22.4 x 328/273

= 26.9L