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Ch.3 - Chemical Reactions and Reaction Stoichiometry
All textbooksBrown 14th EditionCh.3 - Chemical Reactions and Reaction StoichiometryProblem 66b
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Chapter 3, Problem 66b

Calcium hydride reacts with water to form calcium hydroxide and hydrogen gas. (b) How many grams of calcium hydride are needed to form 4.500 g of hydrogen?

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1
Write the balanced chemical equation for the reaction: \( \text{CaH}_2 + 2\text{H}_2\text{O} \rightarrow \text{Ca(OH)}_2 + 2\text{H}_2 \).
Determine the molar mass of hydrogen gas (\( \text{H}_2 \)) using the periodic table. Hydrogen has an atomic mass of approximately 1.01 g/mol, so \( \text{H}_2 \) is about 2.02 g/mol.
Calculate the number of moles of hydrogen gas produced using the given mass (4.500 g) and the molar mass of hydrogen gas: \( \text{moles of } \text{H}_2 = \frac{4.500 \text{ g}}{2.02 \text{ g/mol}} \).
Use the stoichiometry of the balanced equation to find the moles of calcium hydride (\( \text{CaH}_2 \)) needed. According to the equation, 1 mole of \( \text{CaH}_2 \) produces 2 moles of \( \text{H}_2 \).
Calculate the mass of calcium hydride required using its molar mass. First, find the molar mass of \( \text{CaH}_2 \) (Ca: 40.08 g/mol, H: 1.01 g/mol), then use the moles of \( \text{CaH}_2 \) from the previous step to find the mass: \( \text{mass of } \text{CaH}_2 = \text{moles of } \text{CaH}_2 \times \text{molar mass of } \text{CaH}_2 \).
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