Si pour faire un trajet, une voiture consomme 40 litres de...

Si pour faire un trajet, une voiture consomme 40 litres de carburant, quelle masse et quel volume de dioxyde de carbone a-t-elle produits ? > quelle masse et quel volume de dioxygène a-t-elle consommés? > quel volume d'air a été admis dans son moteur? Bien que les carburants soient des mélanges, on admettra qu'il s'agit d'un hydrocarbure $\mathrm{C}_8 \mathrm{H}_{18}$, dont la masse volumique est $0,7 \mathrm{~kg} . \mathrm{L}^{-1}$, et que la réaction de combustion dans le moteur donne exclusivement $\mathrm{CO}_2$ et $\mathrm{H}_2 \mathrm{O}$.

Si pour faire un trajet, une voiture consomme 40 litres de carburant, quelle masse et quel volume de dioxyde de carbone a-t-elle produits ?
> quelle masse et quel volume de dioxygène a-t-elle consommés?
> quel volume d'air a été admis dans son moteur?
Bien que les carburants soient des mélanges, on admettra qu'il s'agit d'un hydrocarbure $\mathrm{C}_8 \mathrm{H}_{18}$, dont la masse volumique est $0,7 \mathrm{~kg} . \mathrm{L}^{-1}$, et que la réaction de combustion dans le moteur donne exclusivement $\mathrm{CO}_2$ et $\mathrm{H}_2 \mathrm{O}$.

Key Concepts

Air Composition and Oxygen Availability

Air is a mixture of gases, primarily nitrogen and oxygen. When considering combustion processes, it is important to account for the fraction of oxygen present in air to determine the total volume of air that must be processed to supply the required oxygen for complete combustion.

Stoichiometry

Stoichiometry involves using a balanced chemical equation to quantitatively relate the amounts (in moles, mass, or volume) of reactants and products. It is fundamental to determining how much of each substance (e.g., carbon dioxide, oxygen) is produced or consumed in a given chemical reaction.

Combustion Reaction

A combustion reaction is a chemical process in which a fuel reacts with an oxidant (usually oxygen) to produce combustion products such as carbon dioxide and water. Understanding the reaction mechanism and the stoichiometric coefficients in these reactions is essential for calculating reactant consumption and product formation.

Mass-Volume Conversions Using Density

Density is the property that relates mass to volume. In problems involving liquid fuels, using density to convert the given volume of fuel into mass is a key step in linking macroscopic measurements with chemical quantities.

Molar Mass and the Mole Concept

The mole concept and molar mass are critical for translating between the mass of a substance and the number of moles, which is a count of entities (atoms, molecules). This conversion is necessary for applying stoichiometric ratios from the balanced equation.

Ideal Gas Law and Gas Volume Determination

The ideal gas law (PV = nRT) connects the number of moles of a gas to its volume under specified conditions. This law is used to calculate the volumes of gases (such as CO2 or oxygen) produced or consumed in a reaction.

Transcript

00:01 This question is quite interesting.

00:03 It is in reference to the volume of the gaseous products that come out of a tellpipe.

00:09 First, it wants to know the total volume in liters of the gaseous products of the combustion reaction, not taking into account the volume of nitrogen and argon yet that is also found in the atmosphere.

00:23 It wants to know this volume at 350 degrees celsius, close to the temperature of the exhaust, and 734 tor, somewhere near atmospheric pressure at a higher elevation than sea level.

00:40 To do this, it suggests using 100 grams of gasoline as your starting amount.

00:49 Gasoline is a mixture of many different compounds, but one that is common to gasoline is octane with a formula c8h18.

00:59 So if it undergoes a combustion analysis, it will react with oxygen, producing carbon dioxide and water.

01:07 It needs to be balanced.

01:09 We have eight carbons, one carbon, so we need to put an eight in front of carbon dioxide.

01:14 We have 18 hydrogens and two hydrogens, so we need to put a two in front of water.

01:20 We now have eight times two, 16 plus nine.

01:24 That gives us 25 oxygens.

01:27 With two oxygens, we need to go.

01:29 25 halves in order to get the 25 oxygens.

01:34 However, we can't leave fractions in a balanced chemical reaction, so we'll multiply everything through by 2, and this will become our balanced chemical reaction.

01:45 So if we start with 100 grams of octane and convert it into moles octane by dividing by the molar mass, we can then use the stoichiometry of the balanced chemical reaction to convert the moles octane into moles of carbon dioxide.

02:03 This is one of the gaseous products...

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