(Originais Teachy 2023) - Question Medium of Chemistry

The search for alternative and more sustainable energy sources has led to the development of fuels composed of mixtures with ideal combustion characteristics. One of the challenges in this process is the improvement of the energy efficiency of internal combustion engines, which depends, in part, on the uniformity of the fuel mixture. Considering an internal combustion engine, where the efficiency of the fuel burning process is directly related to the homogeneity of the air-fuel mixture, a chemical engineer decides to investigate the behavior of different mixtures under pressure and temperature conditions similar to those found in the combustion chamber. For his analysis, he selects two mixtures: the first one is atmospheric air, mainly composed of nitrogen (78%), oxygen (21%), and other gases in lower concentrations, known to be a homogeneous mixture; the second one is a mixture of ethanol and water, in which ethanol and water form two distinct phases due to their differences in polarity and intermolecular interactions, considered a heterogeneous mixture. Based on the concepts of homogeneous and heterogeneous mixtures, which of the two mixtures investigated is more suitable to be used as fuel in an internal combustion engine, considering the goal of maximizing the energy efficiency of the burning process?

To calculate the equilibrium quotient of a chemical reaction, it is necessary to know the concentrations of the chemical species involved at constant temperature and pressure. For example, for the combustion reaction of natural gas (CH4 + 2O2 --> CO2 + 2H2O), what would be the value of the equilibrium constant?

A chemical laboratory received a sample of a new metallic oxide, and the scientists must determine the chemical formula of the compound based on its properties. The sample reacts with water, forming an acid that, when analyzed, reveals the presence of hydrogen and a metal that behaves as a divalent metal in its reactions. Additionally, the sample reacts with diluted hydrochloric acid, forming a metal chloride and water. If the mass of the metal present in the sample is 27g, determine the chemical formula of the metallic oxide and explain the reasoning used, including the nomenclature of the compounds found.