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# Chemistry Question Help Watch

1. Hydrogen and oxygen react according to the following equation.
2H2 + 02 ------>2H2O

If all volumes are measured at 110 °C and one atmosphere pressure, the volume of steam produced after 50 cm3 of hydrogen react completely with 25 cm3 of oxygen is made ?

A) 25cm3

B) 50cm3

C) 75cm3

D) 100cm3

The answer to the question is B but I really dont understand why . All help is much appreciated.
2. (Original post by yousefshah77)
Hydrogen and oxygen react according to the following equation.
2H2 + 02 ------>2H2O

If all volumes are measured at 110 °C and one atmosphere pressure, the volume of steam produced after 50 cm3 of hydrogen react completely with 25 cm3 of oxygen is made ?

A) 25cm3

B) 50cm3

C) 75cm3

D) 100cm3

The answer to the question is B but I really dont understand why . All help is much appreciated.
Look at the number of moles. See if you can make a connection.
Remember that PV=nRT, here P, R, and T are constant - n is an unknown number but the ratio is known.
3. I'm going to give you a verbose mathematical answer here to try and help you understand methodology.

Let's start with the ideal gas law: PV=nRT. With this along side the question, we have constant temperature and pressure, as well as the gas constant. Rearranging with the constants on one side, and noticing that we are asked to calculate volume, an equation that solves for V would be ... ideal (sorry, it had to be done). So, V=(nRT)(P)-1.

With this new equation, we notice that with volume on the left side, and moles on the right side, if the number of moles is halved, for example, then so must the volume of gas.

However, the questions is asking you to give the resulting volume of steam produced, which is equimolar with respect to diatomic hydrogen gas; that is, the same number of moles (two), hence the same volume of gas is produced (50 [cm]3).

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