Stoichiometry propane+oxygen

David Herrera

How to find the balanced Equation for propane+ oxygen

A balanced equation must have equal numbers of each type of atom on both sides of the arrow.An equation is balanced by changing coefficients in a somewhat trial-and-error fashion. It is important to note that only the coefficients can be changed, never a subscript.

C3H8 + 5 O2 ----> 3 CO2 + 4 H2O

Find the molar mass

Use the chemical formula to determine the number of each type of atom present in the compound. Multiply the atomic weight of each element by the number of atoms of that element present in the compound. Add it all together and put units of grams/mole after the number

propane: 44.1 g/mol, oxygen:15.9994 g/mol, carbon dioxide: 44.1 g/mol, water: 18.015 g/mol

Mole to Mole Conversions

Calculate how many moles of a product are produced given quantitative information about the reactants.Then determine the molar relationships of reactants and products in a chemical reaction from the corresponding balanced chemical equation.

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Limiting and Excess Reactant

Limiting Reactant:The reactant in a chemical reaction that limits the amount of product that can be formed. The reaction will stop when all of the limiting reactant is consumed.

Excess reactant:The reactant in a chemical reaction that remains when a reaction stops when the limiting reactant is completely consumed. The excess reactant remains because there is nothing with which it can react.

1 mole C3H8 reacts with 5 moles O2; so the amount of O2 we need to completely reaction with the 3.0 moles of C3H8

3 moles C3H8 x (5 moles O2 / 1 mole C3H8) = 15 moles O2. Since we only have 10 moles O2 and not the 15 we need, O2 is limiting the reaction and C3H8 is in the excess.

Theoretical yield

To determine theoretical yield, multiply the amount of moles of the limiting reagent by the ratio of the limiting reagent and the synthesized product and by the molecular weight of the product.

we consume 10.0 moles O2 x (1 mole C3H8 / 5 moles O2) = 2.0 moles C3H8 and the heat given off 2.0 moles C3H8 x (-2012kJ/mole) = -4024 kJ

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Percent Yield

The percentage yield can be calculated using the mass of the actual product obtained and the theoretical mass of the product calculated using the balanced equation of the reaction.

When oxygen is limiting the reaction, the C3H8 will actually react with the O2 to form CO, CO2 and H2O and without knowing the specifics of the reaction, you can't tell the ratio of CO to CO2

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