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3 years ago

A 20.0 gram sample of an element contains 4.95 x 1023 atoms. what is the element?

1 answer:

7 0

You will want to find how many grams are in a whole mole so you know which element it is. To do this, find out how much of a mole you have.

4.95 x 10^23 atoms / 6.022 x 10^23 atoms (one whole mole of any element) = .8219860511 or ~82% of 1 mole

Now we know that, find what to multiply 20 g by to get the rest of the mole.

1 mole / .8219860511 mole = 1.216565657

20 g x 1.216565657 = ~24.33 g / mol

Now that you have grams per mole, you can look at the periodic table and the molar masses to see which this number is closely aligned.

Your answer is Magnesium (Mg), which has a molar mass of 24.305 g

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a truck start from attains a velocity of 20m/s after 10 second , calculate the acceleration. plz help with this

Marysya12 [62]

Answer:

= u +at

20m/s = 0 + a*10s

a = 20m//10s

a = 2m/s²

From the data given , it is not possible to calculate the displacement , because no direction of motion is given

But it is possible to calculate the distance travelled

Distance = ut + ½ *a*t²

distance = 0 + ½ * 2m/s * 10²s

distance = 100m

3 0

3 years ago

A 150 mL of oxygen gas is collected over water at 20 °C and 758 torr. What volume will the same sample of oxygen occupy at STP w

Stella [2.4K]

Answer:

The volume would be; 136.17 ml

Explanation:

Volume V1 = 150 mL

Temperature T1 = 20°C + 273 = 293 K

Pressure P1 = 758 - 17.54 = 740.46 torr

At STP;

Volume V2 = ?

Pressure P2 = 760 torr

Temperature T2 = 273 K

Using the general gas equation;

P1V1 / T1 = P2V2 / T2

Making V2 subject of formulae;

V2 = P1V1T2 / T1P2

Inserting the values we have;

V2 = 740.46 * 150 * 273 / 293 * 760

V2 = 136.17 ml

3 0

3 years ago

How many moles of H2 can be made from complete reaction of 3.0 moles of Al?

tresset_1 [31]

Answer: 4.5 moles of $H_{2}$ can be made from complete reaction of 3.0 moles of Al.

Explanation:

The given reaction equation is as follows.

$2Al + 6HCl \rightarrow 2AlCl_{3} + 3H_{2}$

This shows that 2 moles of Al reacts with 6 moles of HCl. So, the amount of HCl required to react with 1 mole Al is three times the amount of HCl.

Therefore, 3 moles of Al will react with 9 moles of HCl to give 3 moles of $AlCl_{3}$ and $\frac{9}{2}$ moles of $H_{2}$ .

The reaction equation now will be as follows.

$3Al + 9HCl \rightarrow 3AlCl_{3} + \frac{9}{2}H_{2}$

The moles $\frac{9}{2}$ can also be written as 4.5 moles.

Thus, we can conclude that 4.5 moles of $H_{2}$ can be made from complete reaction of 3.0 moles of Al.

6 0

3 years ago

A decorative "ice" sculpture is carved from dry ice (solid CO2) and held at its sublimation point of –78.5°C. Consider the proce

Leno4ka [110]

Answer:

The answers to the questions are;

a. The entropy of sublimation for carbon dioxide (the system) is

134.07 J/Kmol.

b. The entropy of the universe for this reversible process is 376 J/K.

Explanation:

Entropy of sublimation is the entropy change experienced following the transformation of a mole of solid to vapor at the temperature where the sublimation is taking place

a. We note that the mass of the solid CO₂ = 389 g

Molar mass of CO₂ = 44.01 g/mol

Number of moles of CO₂ in the sculpture = Mass/(Molar mass)

= (389 g)/(44.01 g/mol) = 8.84 Moles

Entropy of sublimation is given by

ΔS $_{sublimation}$ = $S_{vapor}$ - S $_{solid}$ = $\frac{\Delta H_{sublimation}}{T}$