Number of atoms reacting with a gas

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In summary, The equation 4Al + 3O2 = 2Al2O3 involves the reaction of 4 moles of Al with 3 moles of O2 to produce 2 moles of Al2O3. To determine the number of O-atoms that will react with 45dm3 of gas, the formula n=V/Vn (or the law stating that any gas occupies 22.4dm3 at STP) was used to find the number of moles, which was calculated to be 2.01. Then, the formula n=n*Na was used (where Na is Avogadro's Constant) to convert the number of moles to atoms, giving a result of
  • #1
dacoolguy
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Homework Statement


4Al + 3O2 = 2Al2O3
What number of O-atoms will react if 45dm3 of the gas reacts with an excess of Al?
The answer is apparently: 4 atoms

Homework Equations





The Attempt at a Solution


Using the formula n=V/Vn (or the law stating that any gas occupies 22.4dm3 at STP), I found that the number of moles was (225/112) or 2.01. Then I used the formula: n=n*Na (number of moles times Avagadro's Constant) giving me 1.24*1024 atoms. Where did I go wrong please?
 
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  • #2
The answer is not 4 atoms.

I have no idea what 225/112 means, even if the number of moles seems to correct.

You have 45 L of the gas, there is 22.4 L per mole - how many moles of the gas?

You have correctly converted number of moles of gas to number of molecules, however, you forgot that there is more than one atom per molecule.
 
  • #3


Your approach is correct, but you made a mistake in calculating the number of moles. The correct calculation should be n = V/Vn = (45/22.4) = 2.01 moles of gas. This means that there are 2.01 moles of O2 reacting, which corresponds to 2.01*6.02*10^23 = 1.21*10^24 O-atoms reacting. This is equivalent to 4 atoms (since the reaction ratio is 4:3 for Al:O2). Therefore, the answer of 4 atoms is correct.
 

1. How is the number of atoms reacting with a gas determined?

The number of atoms reacting with a gas is determined by measuring the number of moles of the gas present in the reaction and using Avogadro's number (6.022 x 10^23) to calculate the number of atoms.

2. Does the temperature and pressure of the gas affect the number of atoms involved in the reaction?

Yes, the temperature and pressure of the gas can affect the number of atoms involved in the reaction. As the temperature and pressure increase, the molecules of the gas become more energetic and move faster, leading to more collisions and a higher chance of reactions occurring.

3. Can the number of atoms reacting with a gas change during the course of a reaction?

Yes, the number of atoms reacting with a gas can change during the course of a reaction. As the reaction progresses, some molecules may be consumed while others may be produced, leading to a change in the number of atoms involved.

4. How is the number of atoms reacting with a gas related to the rate of the reaction?

The number of atoms reacting with a gas is directly related to the rate of the reaction. As the number of atoms involved increases, there are more collisions and a higher chance of successful reactions occurring, leading to a faster reaction rate.

5. Can the number of atoms reacting with a gas be controlled?

Yes, the number of atoms reacting with a gas can be controlled by adjusting the amount of gas present in the reaction and the reaction conditions such as temperature and pressure. This can also be achieved by using catalysts to increase the rate of the reaction, resulting in more atoms being involved in a shorter period of time.

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