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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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: \( \text{mass of } \text{CaH}_2 = \text{moles of } \text{CaH}_2 \times \text{molar mass of } \text{CaH}_2 \).

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 chemists to calculate the amounts of substances consumed and produced in a reaction based on balanced chemical equations. Understanding stoichiometry is essential for determining how much of a reactant is needed to produce a desired amount of product.

Molar Mass

Molar mass is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). It is calculated by summing the atomic masses of all the atoms in a molecule. Knowing the molar mass of calcium hydride (CaH2) is crucial for converting between grams and moles, which is necessary for stoichiometric calculations in the given reaction.

Balanced Chemical Equation

A balanced chemical equation represents a chemical reaction with equal numbers of each type of atom on both sides of the equation. It ensures the law of conservation of mass is upheld. For the reaction between calcium hydride and water, the balanced equation is CaH2 + 2H2O → Ca(OH)2 + H2, which provides the necessary ratios of reactants and products to perform stoichiometric calculations.

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