Textbook Question
Calculate how many moles of NH3 form when each quantity of reactant completely reacts. 3 N2H4(l) → 4 NH3(g) + N2(g) c. 65.3 g N2H4
Ch.4 - Chemical Reactions and Chemical Quantities
Chapter 4, Problem 31
Hydrobromic acid dissolves solid iron according to the reaction:
Fe(s) + 2 HBr(aq) → FeBr2(aq) + H2(g)
What mass of HBr (in g) do you need to dissolve a 3.2-g pure iron bar on a padlock? What mass of H2 would the complete reaction of the iron bar produce?
Verified step by step guidance1
Determine the molar mass of iron (Fe) and hydrobromic acid (HBr).
Calculate the number of moles of iron in the 3.2-g iron bar using its molar mass.
Use the stoichiometry of the balanced chemical equation to find the moles of HBr needed. The equation shows that 1 mole of Fe reacts with 2 moles of HBr.
Convert the moles of HBr to grams using the molar mass of HBr.
Calculate the moles of H2 produced using the stoichiometry of the reaction, where 1 mole of Fe produces 1 mole of H2, and then convert this to grams using the molar mass of H2.
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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 calculation of reactants and products in chemical reactions based on the balanced chemical equation. It allows us to determine the relationships between the amounts of substances involved in a reaction, using mole ratios derived from the coefficients in the balanced equation. In this case, it helps us find the mass of HBr needed to react with a given mass of iron and the mass of hydrogen gas produced.
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Stoichiometry Concept
Molar Mass
Molar mass is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). It is essential for converting between the mass of a substance and the number of moles, which is necessary for stoichiometric calculations. For this problem, knowing the molar masses of iron (Fe) and hydrobromic acid (HBr) will allow us to calculate the required mass of HBr and the mass of hydrogen gas produced.
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Gas Laws
Gas laws describe the behavior of gases under various conditions of temperature and pressure. In this context, while the production of hydrogen gas (H2) is a result of the reaction, understanding gas laws can help predict how the gas behaves after formation. Although not directly required for mass calculations, it provides insight into the properties of the gas produced in the reaction.
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Related Practice
Textbook Question
Consider the balanced equation:
SiO2(s) + 3 C(s) → SiC(s) + 2 CO(g)
Complete the table showing the appropriate number of moles of reactants and products. If the number of moles of a reactant is provided, fill in the required amount of the other reactant, as well as the moles of each product that forms. If the number of moles of a product is provided, fill in the required amount of each reactant to make that amount of product, as well as the amount of the other product that forms.
Textbook Question
Consider the balanced equation:
SiO2(s) + 3 C(s) → SiC(s) + 2 CO(g)
Complete the table showing the appropriate number of moles of reactants and products. If the number of moles of a reactant is provided, fill in the required amount of the other reactant, as well as the moles of each product that forms. If the number of moles of a product is provided, fill in the required amount of each reactant to make that amount of product, as well as the amount of the other product that forms.
Textbook Question
Hydrobromic acid dissolves solid iron according to the reaction:
Fe(s) + 2 HBr(aq) → FeBr2(aq) + H2(g)
What mass of HBr (in g) do you need to dissolve a 3.2-g pure iron bar on a padlock?
Textbook Question
For each of the reactions, calculate the mass (in grams) of the product that forms when 15.39 g of the underlined reactant completely reacts. Assume that there is more than enough of the other reactant.
a. 2 K(s) + Cl2(g) → 2 KCl(s)
b. 2 K(s) + Br2(l) → 2 KBr(s)
c. 4 Cr(s) + 3 O2(g) → 2 Cr2O3(s)
d. 2 Sr(s) + O2(g) → 2 SrO(s)
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