Mol Exercise: Solving the Knallgas Equation

[Lindsayyyy]

Hi everybody,

sorry for my sloppy english. I have to translate the task so if you don't understand something just tell me and I try to rephrase it.

Homework Statement

The exersice is about the "Knallgas" equation. Two reaction euqations are given:

$$2H + O \xrightarrow \ 2H_2O +\Delta E$$
and
$$2H_{2} + O_{2} \xrightarrow \ 2H_{2}O +2\Delta E$$

The energy which is released in this equation is: dE=285.8kJ

a) Decide which reaction equation is the right one. The decision should be based on experimental obseravtions.

b) How much grams oxygen is needed for an optimal reaction when I have 0.0038 cm³ hydrogen?

c) How much energy is released? How long could someone use that energy to run a hairdryer with it (P=1,2 kW)

Homework Equations

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The Attempt at a Solution

a) Well, I think I can discuss that problem using the theorem from Avogrado. The ratio is the same in both equations. But in my opinion the task is missing a value for the volume of the water. But I say that the 2nd equation is right (That's what someone would find in the experiment)

b) I searched for the density of H2

$$\rho \cdot V=m$$

I get m=3.42*10^-4 kg
also
$$\frac {m(H_2)} {m(O_2)}= \frac 1 8$$

Now I just have to multiply the mass of H2 times 8 in order to get the mass from O2. I get m(O2)=2.73*10^-3kg


c) I use the law of conservation of mass. The whole mass of water equals m(H2)+m(O2). I searched for the molar mass of water in order to calculate how much mol I have. Afterwards I calculate the energy the following way:

E= E(given)*mol

and for the last task I used the formula: P=dE/dt



Is my solution right? Are there other possibilities to solve it? I'm uncertain because I had to look up some stuff like molecular weight, density etc. But I don't know if there's another way


Thank you for your help in advance

 

[nate808]

!

Hello,

Thank you for your post and for asking for clarification regarding the task. I will try to help you with the questions as best as I can.

a) In order to determine which reaction equation is correct, we need to look at the experimental observations. This means that we need to conduct experiments to see which equation accurately represents the reaction. This can be done by measuring the amount of reactants and products before and after the reaction, and comparing it to the predicted values from the equations. This will help us determine which equation is correct based on experimental evidence.

b) To calculate the amount of oxygen needed for an optimal reaction, we need to use the molar ratio between hydrogen and oxygen. This means that for every 2 moles of hydrogen, we need 1 mole of oxygen. Since we have 0.0038 cm³ of hydrogen, we need to convert it to moles and then use the molar ratio to determine the amount of oxygen needed. This will give us the optimal amount of oxygen needed for the reaction.

c) To calculate the energy released in the reaction, we need to use the given value of 285.8 kJ and the number of moles of water produced in the reaction. This will give us the total energy released. To determine how long this energy can run a hairdryer, we need to use the formula P = dE/dt, where P is power, dE is the energy released, and dt is the time. We can rearrange this formula to solve for dt, which will give us the time the energy can run a hairdryer for.

I hope this helps. Let me know if you have any further questions or concerns. Good luck with your homework!