Ethanol \(\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\right)\) is blended with gasoline as an automobile fuel. (a) Write a balanced equation for the combustion of liquid ethanol in air. (b) Calculate the standard enthalpy change for the reaction, assuming \(\mathrm{H}_{2} \mathrm{O}(g)\) as a product. (c) Calculate the heat produced per liter of ethanol by combustion of ethanol under constant pressure. Ethanol has a density of 0.789 \(\mathrm{g} / \mathrm{mL}\) (d) Calculate the mass of \(\mathrm{CO}_{2}\) produced per ky of heat emitted.

Understanding the concept of enthalpy change is crucial when dealing with reactions like the combustion of ethanol. Enthalpy change, represented as \(\Delta H\text{rxn}\), is the amount of heat released or absorbed during a chemical reaction at constant pressure.
To comprehend the enthalpy change for the combustion of ethanol, you consider both the reactants and products. According to the law of conservation of energy, the energy required to break the chemical bonds in the reactants is different from the energy released when new bonds form in the products.
The standard enthalpy change for a reaction is calculated using standard enthalpies of formation \(\Delta H_f^\circ\), which represent the heat change when one mole of a compound is formed from its elements in their standard states.

Calculating Standard Enthalpy Change

The standard enthalpy change for the combustion of ethanol is found by subtracting the enthalpy of the reactants from that of the products. The formula is: \[\Delta H_{\text{rxn}}^\circ = \Sigma n_i\Delta H_{f,i}^\circ(\text{products}) - \Sigma n_j\Delta H_{f,j}^\circ(\text{reactants})\]Here, \(n_i\) and \(n_j\) are the stoichiometric coefficients from the balanced chemical equation. For the combustion of ethanol, this process typically shows energy is released, indicating that the reaction is exothermic.

Stoichiometry is the mathematical relationship between the amounts of reactants and products in a chemical reaction. It is a key concept in ensuring chemical equations are balanced with respect to mass and charge.
Stoichiometry involves calculations based on the molar ratios depicted in a balanced chemical equation. For the combustion of ethanol, we use stoichiometry to reveal that one mole of ethanol reacts with three moles of oxygen to produce two moles of carbon dioxide and three moles of water.

Applying Stoichiometry to Calculate Heat Production

The problem at hand requires calculating the heat produced per liter of ethanol. Using its density, you first determine the mass and then convert this into moles. And since the enthalpy change of the reaction is known, stoichiometry allows you to calculate the heat produced from a known quantity of ethanol.
Issues like density conversions, molar mass calculations, and understanding the combustion process become less daunting when you get a solid grip on stoichiometry. This pillar of chemistry doesn't just apply to ethanol combustion; it's the backbone for all quantitative analysis in chemical reactions.

Chemical equations are symbolic representations of chemical reactions, showcasing the reactants and products along with their respective quantities. Getting familiar with writing chemical equations involves understanding the reactants involved, predicting the products, and balancing the equation.
For the combustion of ethanol, the equation begins with ethanol \(C_2H_5OH\) and oxygen gas \(O_2\). The products of this combustion are carbon dioxide \(CO_2\) and water \(H_2O\), which for our purposes is considered in its gaseous state.

Balancing the Combustion Equation

The chemical equation for the combustion of ethanol is balanced by adjusting the coefficients to ensure an equal number of atoms of each element on both sides of the equation:\[C_2H_5OH (l) + 3O_2 (g) \rightarrow 2CO_2 (g) + 3H_2O (g)\]Balancing chemical equations is a foundational skill in chemistry that confirms the law of conservation of mass. It ensures that the quantity of each element does not change in the reaction. Learning to write and balance equations like this one for ethanol's combustion aids in understanding the reaction process and is essential for thorough chemical analysis.