1. Chromium metal reacts with oxygen to give chromium(III) oxide, Cr2O3. Write a

Question

1.

Chromium metal reacts with oxygen to give chromium(III) oxide, Cr2O3. Write a balanced equation for the reaction. What mass (in grams) of Cr2O3 is produced if 0.190 g of chromium metal is converted completely to the oxide? What mass of O2 (in grams) is required for the reaction?

_____g Cr2O3

_____g O2

2.

The reaction of methane and water is one way to prepare hydrogen for use as a fuel:

CH4(g) + H2O(g) CO(g) + 3 H2(g)

What is the maximum mass of H2 that can be prepared if the mass of CH4 is 1230 g, the mass of water is 1130 g, and H2O is the limiting reactant?

______ g H2

Explanation / Answer

1) Balanced Reaction

2Cr(s) + 3O2(g) -------- Cr2O3s)

2 moles of Cr will give 1 mole of Cr2O3

Moles of Chromium = 0.190/52 = 0.0036538 moles

Moles of Cr2O3 formed = 0.0036538/2 = 0.0018269 moles

Molar mass of Cr2O3 = 2 * 52 + 48 = 152 gm/mol

Mass of Cr2O3 formed = 0.0018269 moles * 152 gm/mol = 0.2776 grams

2)

CH4(g) + H2O(g) ----- CO(g) + 3H2(g)

Number of moles of water = 1130/18 = 62.777 moles

Since water is the limiting reagent

1 mole of H2O gives 3 moles of H2

Moles of H2 formed = 3 * 62.77778 = 188.333 moles

Mass of H2 formed = 188.333 mol * 2 gm/mol = 376.66 grams

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