Determining Limiting Reactants

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In summary, the reaction between 0.80 mol CaH2 and 1.29 mol H2O will produce 0.645 mol of H2 gas, based on the balanced equation and the molar ratio of 2:1. However, the limiting reactant must be determined to accurately calculate the amount of H2 produced.
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Homework Statement


The reaction of calcium hydride and water produces calcium hydroxide and hydrogen as products. How many moles of H2 gas will be formed in the reaction between 0.80 mol CaH2 solid and 1.29 mol H2O liquid? (Two Significant Digits):



Homework Equations





The Attempt at a Solution


Well the balanced equation for this reaction I believe is CaH2 + 2H2O -> Ca(OH)2 + H2. Therefore the molar ration is about 2:1 so if 1.29 mol is reacts than 0.645 will be formed? But I'm always wrong? Any help is appreciated.
 
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  • #2
You need 2 moles of water to 1 mole of CaH2. What ratio of reactants do you have? How does 1.29:0.80 compare with 2:1 ? Now, which is the limiting reactant? This is then what you use to determine the amount of hydrogen produced.
 
  • #3


Your approach is correct. The molar ratio of CaH2 to H2 is 1:1, so for every 1 mol of CaH2 that reacts, 1 mol of H2 is produced. Therefore, with 0.80 mol of CaH2, 0.80 mol of H2 will be produced. However, since the question asks for the number of moles of H2 produced from 1.29 mol of H2O, you need to use the molar ratio of CaH2 to H2O, which is 1:2. This means that for every 1 mol of CaH2 that reacts, 2 mol of H2O is needed. So for 1.29 mol of H2O, 0.645 mol of CaH2 is needed. Since there is only 0.80 mol of CaH2 available, it will be the limiting reactant and only 0.645 mol of H2 will be produced.
 

1. What is a limiting reactant?

A limiting reactant is the substance that is completely consumed in a chemical reaction, thereby limiting the amount of product that can be formed.

2. How do you determine the limiting reactant in a chemical reaction?

To determine the limiting reactant, you must compare the amounts of each reactant present in the reaction. The reactant with the smallest number of moles is the limiting reactant.

3. What is the purpose of determining the limiting reactant?

Determining the limiting reactant allows you to predict the maximum amount of product that can be formed in a reaction, as well as the amount of excess reactant that will be left over.

4. Can the limiting reactant change in a reaction?

Yes, the limiting reactant can change depending on the amounts of each reactant present and the stoichiometry of the reaction.

5. How does the concept of limiting reactants relate to the Law of Conservation of Mass?

The concept of limiting reactants is based on the Law of Conservation of Mass, which states that matter cannot be created or destroyed in a chemical reaction. The limiting reactant is the one that is completely consumed, meaning that all of its atoms are accounted for in the products.

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