Question 5-3 Avogadro\'s law implies that, the ratio of volumes of gaseous react

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Question 5-3

Avogadro's law implies that, the ratio of volumes of gaseous reactants and products that are involved in a reaction, is same as ratio of number of moles (or number of molecules) of the reactants and products, under same conditions of temperature and pressure.

The ratio of number of moles (or number of molecules) of the reactants and products is given by ratio of the respective stoichiometric coefficients in the balanced chemical equation.

Hence, under same conditions of temperature and pressure, the ratio of gaseous reactants and products are given by ratio of stoichiometric coefficients in the balanced chemical equation for the reaction.

According to the given balanced chemical equation,

1 mole of N2 reacts with 3 mole of H2 to form 2 mole of NH3

If n1, n2 and n3 are number of moles of N2, H2 and NH3, then, ratio of number of moles of gaseous reactants and products in this reaction is,

n1 : n2 : n3 = 1 : 3 : 2

If V1, V2 and V3 are volumes of N2, H2 and NH3 (under same conditions of temperature and pressure), involved in the reaction, then, according to Avogadro's law, ratio of volumes of the gases is same as ratio of number of moles which is same as ratio of stoichiometric coefficients in the balanced chemical equation.

V1 : V2 : V3 = n1 : n2 : n3 = 1 : 3 : 2

According to the balanced chemical equation,

3 mole of hydrogen on reaction yields 2 mole of ammonia

So, 3 volumes of hydrogen on reaction yields 2 volumes of ammonia

(provided the volumes are considered under same conditions of temperature and pressure)

Therefore, 3 Liters of hydrogen upon reaction yields 2 Liters of ammonia

So, 7.5 Liters of of hydrogen upon reaction yields, 7.5 L * 2 L / 3 L = 5 L of ammonia

ANSWER: 5 Liters of ammonia form when 7.5 Liters of hydrogen reacts.

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Question 5-4

Consider a gaseous mixture for which the total pressure is Ptotal. Let the partial pressures of the individual gases be, P1, P2, P3,.......Pi.

According to Dalton's Law of partial pressures,

Ptotal = P1 + P2 + P3 +.......+ Pi

Solution to given problem,

Gas mixture contains, helium (He), oxygen (O2) and nitrogen (N2).

Total pressure of gas mixture, Ptotal = 12 atm

Partial pressure of helium, PHe = 2 atm

Partial pressure of oxygen, PO2= 3 atm

Let partial pressure of nitrogen be PN2

According to Dalton's law of partial pressures,

Ptotal = PHe + PO2 + PN2

So, 12 atm = 2 atm + 3 atm + PN2

Therefore, PN2 = 7 atm

Hence, partial pressure of nitrogen gas is 7 atm.

ANSWER: Partial pressure of nitrogen gas is 7 atm.

Explanation / Answer

C. Avogadro's Law Equal volumes of different gases, if measured at the same temperature and pressure, contain equal numbers of gas molecules Hence, can do stoichiometry (ratio) calculations based on a balanced equation in volume units so long as the gases are measured at the same temperature and pressure 5-3 For the reaction given below, how many ters of ammonia form when 7.5 Aters of hydrogen reacts? N2 (g) 3 H2 (g) --> 2 NH3(g) + D. Dalton's Law of Partial Pressures The total pressure of a gas is a simple sum of the partial pressures of the individual gases that are present in the gas mixture. 5-4 A gas mixture containg helium, oxygen, and nitrogen has a total pressure of 12 atm. If the helium has a partial pressure of 2 atm and the oxygen has a partial pressure of 3 atm, what is the partial pressure of the nitrogen gas?

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