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Vesna [10]
2 years ago
10

If you have 100 grams of a radioactive isotope with a half life of 10 years how much of the isotope will you have left after 20

years
Chemistry
1 answer:
Cerrena [4.2K]2 years ago
3 0

Hey there!

A half-life means after a certain amount of time, half of that substance will be gone/changed after that time.

There are two half lives in 20 years because 20 ÷ 10 = 2.

So, we divide the 100g sample in half 2 times.

100 ÷ 2 = 50

50 ÷ 2 = 25

There will be 25g of the radioactive sample remaining after two half lives.

Hope this helps!

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Hydrogen gas (a potential future fuel) can be formed by the reaction of methane with water according to the following equation:
dem82 [27]

Answer:

The percent yield of the reaction is 62.05 %

Explanation:

Step 1: Data given

Volume of methane = 25.5 L

Pressure of methane = 732 torr

Temperature = 25.0 °C = 298 K

Volume of water vapor = 22.0 L

Pressure of H2O = 704 torr

Temperature = 125 °C

The reaction produces 26.0 L of hydrogen gas measured at STP

Step 2: The balanced equation

CH4(g) + H2O(g) → CO(g) + 3H2(g)

Step 3: Calculate moles methane

p*V = n*R*T

⇒with p = the pressure of methane = 0.963158 atm

⇒with V = the volume of methane = 25.5 L

⇒with n = the moles of methane = TO BE DETERMINED

⇒with R = the gas constant = 0.08206 L*atm/mol*K

⇒with T = the temperature = 298 K

n = (p*V) / (R*T)

n = (0.963158 * 25.5 ) / ( 0.08206 * 298)

n = 1.0044 moles

Step 4: Calculate moles H2O

p*V = n*R*T

⇒with p = the pressure of methane = 0.926316 atm

⇒with V = the volume of methane = 22.0 L

⇒with n = the moles of methane = TO BE DETERMINED

⇒with R = the gas constant = 0.08206 L*atm/mol*K

⇒with T = the temperature = 398 K

n = (p*V) / (R*T)

n = (0.926316 * 22.0) / (0.08206 * 398)

n = 0.624 moles

Step 5: Calculate the limiting reactant

For 1 mol methane we need 1 mol H2O to produce 1 mol CO and 3 moles H2

H2O is the limiting reactant. It will completely be consumed (0.624 moles).

Methane is in excess. There will react 0.624 moles. There will remain 1.0044 - 0.624 moles = 0.3804 moles methane

Step 6: Calculate moles hydrogen gas

For 1 mol methane we need 1 mol H2O to produce 1 mol CO and 3 moles H2

For 0.624 moles H2O we'll have 3*0.624 = 1.872 moles

Step 9: Calculate volume of H2 at STP

1.0 mol at STP has a volume of 22.4 L

1.872 moles has a volume of 1.872 * 22.4 = 41.9 L

Step 10: Calculate the percent yield of the reaction

% yield = (actual yield / theoretical yield) * 100 %

% yield = ( 26.0 L / 41.9 L) *100 %

% yield = 62.05 %

The percent yield of the reaction is 62.05 %

6 0
3 years ago
Read 2 more answers
Which formula can be used to find velocity if kinetic energy and mass are known?
astraxan [27]

Answer:

v =  \sqrt{ \frac{2ke}{m} }

option D is the correct option.

Here,

If an object of mass 'm' moving with a velocity'v' then,

kinetic \: energy =  \frac{1}{2} m {v}^{2}  \\  \:  \:  \:  \:  \:  \:  \:  \:  \:  \:  \:  \:  \:  \:  \:  \:  \:  \:  \:  \:  \:  \:  \:  \:  \:  \:  \:  \:  \:    {v}^{2}  =  \frac{2ke}{m}  \\  \:  \:  \:  \:  \:  \:  \:  \:  \:  \:  \:  \:  \:  \:  \:  \:  \:  \:  \:  \:  \:  \:  \:  \:  \:  \:  \:  \:  \:  \:  \:  \:  {v}^{2}  =  \sqrt{ \frac{2ke}{m} }

hope this helps...

Good luck on your assignment..

5 0
3 years ago
You have decided to bake a cake. You mix all of your ingredients together to make a delicious chocolate cake. Then, you bake you
Lapatulllka [165]

Answer:

A gas is evolved

The ingredients can not be recovered

Explanation:

A chemical change is one in which a new substance is formed and it is not easily reversible.

One major ingredient used in cake baking is the baking powder or baking soda.

Baking a cake can be viewed as a chemical change. This is because, when the baking powder or soda is added in the presence of yeast, carbon dioxide gas is evolved as tiny bubbles of gas which makes the cake light and fluffy. Heat is equally given off in the process. The baking powder and other cake ingredients can not be recovered, hence, we can conclusively assert that a chemical change has taken place.

3 0
3 years ago
Ms. Garcia's science students are studying scale models. For her science project, Sarah has decided to make a scale model of the
strojnjashka [21]

Answer:

D. 109 cm

hope this helped :)

8 0
3 years ago
Read 2 more answers
How many grams of a 14.0% (w/w) sugar solution contain 62.5<br> of sugar?
Delicious77 [7]

Answer:

m_{solution}=446.4g

Explanation:

Hello,

In this case, by-mass percent is computed in terms of the mass of the solute and the mass of the solvent as shown below:

\% m=\frac{m_{solute}}{m_{solution}} *100\%

Thus, solving for the mass of the solution, we obtain:

\frac{x}{y} m_{solution}=\frac{m_{solute}}{\% m}*100\%\\ \\m_{solution}=\frac{62.5g}{14.0\%}*100\% \\\\m_{solution}=446.4g

Regards.

3 0
3 years ago
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