A mixture of N21g2 and H21g2 reacts in a closed container to form ammonia, NH31g2. The reaction ceases before either reactant has been totally consumed. At this stage 3.0 mol N2, 3.0 mol H2, and 3.0 mol NH3 are present. How many moles of N2 and H2 were present originally?

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insert step 1> Write the balanced chemical equation for the reaction: N_2(g) + 3H_2(g) \rightarrow 2NH_3(g).

insert step 2> Use the stoichiometry of the reaction to set up relationships between the moles of reactants and products. For every 1 mole of N_2, 3 moles of H_2 are required to produce 2 moles of NH_3.

insert step 3> Let x be the initial moles of N_2 and y be the initial moles of H_2.

insert step 4> Set up the equations based on the stoichiometry and the information given: x - a = 3.0 (moles of N_2 remaining), y - 3a = 3.0 (moles of H_2 remaining), and 2a = 3.0 (moles of NH_3 formed).

insert step 5> Solve the system of equations to find the initial moles of N_2 (x) and H_2 (y).

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Stoichiometry

Stoichiometry is the branch of chemistry that deals with the quantitative relationships between the reactants and products in a chemical reaction. It allows us to calculate the amounts of substances consumed and produced in a reaction based on balanced chemical equations. In this case, understanding the stoichiometric ratios of nitrogen (N2), hydrogen (H2), and ammonia (NH3) is essential to determine the original amounts of reactants.

Limiting Reactant

The limiting reactant is the substance that is completely consumed in a chemical reaction, thus determining the maximum amount of product that can be formed. In this scenario, identifying which reactant (N2 or H2) limits the formation of NH3 is crucial for calculating the initial moles of each reactant. The limiting reactant concept helps in understanding how much of each reactant was present before the reaction reached equilibrium.

Chemical Equilibrium

Chemical equilibrium occurs when the rates of the forward and reverse reactions are equal, resulting in constant concentrations of reactants and products. In this problem, the reaction between N2 and H2 to form NH3 reaches a point where the amounts of all species remain unchanged. Recognizing that the reaction has not gone to completion but has reached a state of equilibrium is vital for determining the initial amounts of N2 and H2.

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