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olya-2409 [2.1K]
3 years ago
12

;_; help please i need help TwT

Chemistry
2 answers:
Airida [17]3 years ago
6 0

Answer:

it's a day I think so ........

Tems11 [23]3 years ago
3 0

Answer:

Lunar cycle

Explanation:

Year is the amount of time for the Earth to rotate a complete circle around the sun.

Lunar cycle (moon phases) is the rotation of the Moon around the Earth.

Day is the time for the Earth to rotate on its own axis completely.

Solar cycle is the changes that the sun's electric field goes through about every 11 years.

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A solution contains 50.0g of heptane (C7H16)and 50.0g of octane (C8H18) at 25 degrees C.The vapor pressures of pure heptane and
AleksandrR [38]

Answer:

a)Pheptane = 24.3 torr          

Poctane = 5.12 torr    

b)Ptotal vapor = 29.42 torr

c)  81 % heptane

    19 % octane

d) See explanation below

Explanation:

The partial pressure is given by Raoult´s law as:

Pa = Xa Pºa where Pa = partial pressure of component A

                               Xa = mole fraction of A

                               Pºa = vapor pressure of pure A

For a binary solution what we have to do is compute the partial  vapor pressure of each component and then add them together to get total vapor pressure.

In order to calculate the composition of the vapor  in part b), we will first calculate the mole fraction of each component in the vapor which is given by the relationship:

          Xa = Pa/Pt where Xa = mol fraction of  in the vapor

                                       Pa = partial pressure of A as calculated above

                                        Pt = total vapor pressure

Once we have mole fractions we can calculate the masses of the components for part c)    

a)                  

 MW heptane = 100.21 g/mol

 MW octane = 114.23 g/mol

mol heptane = 50.0 g / 100.21 g/mol = 0.50 mol

mol octane = 50.0 g/ 114.23 g/mol = 0.44 mol

mol total = 0.94 ⇒ Xa= 0.50/0.94 = 0.53 and

                             Xb= 0.44/0.94 = 0.47

Pheptane = 0.53 x 45.8 torr = 24.3 torr

Poctane = 0.47 x 10.9 torr = 5.12 torr

b) Ptotal = 24.3 torr +5.12 torr = 29.42 torr

c) We will call Y the mole fraction in the vapor to differentiate it from the mole fraction in solution

Y heptane (in the vapor) = 24.3 torr/ 29.42 torr = 0.83

Y octane (in the vapor) = 5.12 torr/ 29.42 torr = 0.17

d) To solve this part   we will assume that since the molecular weights are similar then having a mole fraction for heptane of 0.82, we could say that for every mole of mixture we have 0.82 mol heptane and 0.17 mol octane  and then we can calculate the masses:

0.82 mol x 100.21  g/mol = 82.2 g

0.17 mol x 114.23 g/mol =  19.4 g

total mass = 101.6

% heptane = 82.2 g/101.6g x 100 = 81 %

% octane = 19 %

There is another way to do this more exactly by calculating the average molecular weight of the mixture:

average MW = 0.83 (100.21 g/mol)  + 0.17 ( 114.23 g/mol ) = 102. 6 g/mol

and then  having a mol fraction of 0.83  means in 1 mol of mixture we have 0.83 mol heptane and 0.17 mol octane then the masses are:

mass heptane = 0.83 x 100.21 g/mol = 83.2 g

mass octane = 0.17 x  114.23 g/mol = 19.4 g

mass of mixture = 1 mol x MW mixture = 1 mol x 102.6 g/mol 102.6 g

% heptane = (83.2 g/ 102.6 g ) x 100 g = 81 %

% octane = 100 - 81 = 19 %

d)The composition of the vapor is different from the composition of the solution because the vapor is going to be richer in the more volatile compound in the solution which in this case is heptane ( 45.8  vs 10.9 torr).

4 0
3 years ago
How many atoms are in 1.15 mole Cu?
xxMikexx [17]
6.022x10^23 is Avogadro’s number. Use this whenever you work with Stoichiometry involving Atoms, formula units, or molecules. 1 mol of anything is always Avogadro’s number.

Multiply everything on the top= 6.93 x 10^23
Divide by everything on the bottom = 6.93 x 10^23
Answer: 6.93 x 10^23 atoms Cu.

4 0
3 years ago
Read 2 more answers
811.68 J of energy are used on a 95g chunk of unknown metal. Calculate the resulting temperature change if the specific heat of
Ivan

Answer:

16 °C

Explanation:

Step 1: Given data

  • Provided heat (Q): 811.68 J
  • Mass of the metal (m): 95 g
  • Specific heat capacity of the metal (c): 0.534 J/g.°C

Step 2: Calculate the temperature change (ΔT) experienced by the metal

We will use the following expression.

Q = c × m × ΔT

ΔT = Q/c × m

ΔT = 811.68 J/(0.534 J/g.°C) × 95 g = 16 °C

6 0
3 years ago
Clouds are formed by the ________ water
tatuchka [14]
Clouds are made of water. When water evaporates it turns into clouds. So, I think the answer is EVAPORATED water.
4 0
3 years ago
How are nymphs different from adult insects?
umka2103 [35]

Answer:

Explanation:

the nymph looks like a smaller version of the adult insect, & it also has no wings & molts.

4 0
3 years ago
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