gas evolution reaction

Examples of gas evolution reaction in the following topics:

• Gas Evolution Reactions

  • A gas evolution reaction is a chemical process that produces a gas, such as oxygen or carbon dioxide.
  • A gas evolution reaction is a chemical process that produces a gas, such as oxygen or carbon dioxide.
  • The oxidation of a metal in acidic solution will yield a metal salt and hydrogen gas:
  • The oxidation of metals by strong acids is another common example of a gas evolution reaction.
  • Hydrochloric acid oxidizes zinc to produce an aqueous metal salt and hydrogen gas bubbles.

• Substitution of the Hydroxyl Hydrogen

  • This is the procedure used in reactions 2 and 3.
  • This toxic and explosive gas is always used as an ether solution (bright yellow in color).
  • The reaction is easily followed by the evolution of nitrogen gas and the disappearance of the reagent's color.
  • The mechanisms of reactions 1 & 4 will be displayed in the second diagram below.
  • Examples of these reactions are displayed in the third diagram above.

• Writing Chemical Equations

  • A chemical equation is the symbolic representation of a chemical reaction.
  • For example, a compound in the gas state would be indicated by (g), solid (s), liquid (l), and aqueous (aq).
  • Symbols are used to differentiate among different types of reactions.
  • If the reaction requires energy, it is often indicated above the arrow.
  • When a baking soda volcano is made by mixing vinegar (dilute aqueous acetic acid) and baking soda (sodium bicarbonate), the resulting evolution of gas occurs via the following reaction:

• The Arndt-Eistert Reaction

  • When an ether solution of diazomethane is slowly added to a warm solution of the acid chloride, nitrogen evolution is observed and the chloromethyl ketone is the chief product.
  • One equivalent of diazomethane is required for this reaction.
  • The products are the diazo ketone and methyl chloride (a gas) from the reaction of diazomethane with HCl.
  • The first two examples are typical Arndt-Eistert reactions.
  • Reaction #3 is an example of such an alternative reaction.

• Expressing the Equilibrium Constant of a Gas in Terms of Pressure

  • For gas-phase reactions, the equilibrium constant can be expressed in terms of partial pressures, and is given the designation KP.
  • Take the general gas-phase reaction:
  • In this expression, $\Delta n$ is a measure of the change in number of moles of gas in the reaction.
  • For instance, if a reaction produces three moles of gas, and consumes two moles of gas, then $\Delta n=(3-2)=1$.
  • Write the equilibrium expression, KP, in terms of the partial pressures of a gas-phase reaction

• Gas Stoichiometry

  • At standard temperature and pressure, one mole of any gas will occupy a volume of 22.4 L.
  • Stoichiometry is the quantitative study of the relative amounts of reactants and products in chemical reactions; gas stoichiometry involves chemical reactions that produce gases.
  • According to the above reaction, what volume of NO2(g) is produced from the combustion of 100 g of NH3(g), assuming the reaction takes place at standard temperature and pressure?
  • Shows how to use stoichiometry to convert from grams of a gas to liters of a gas.
  • Calculate volumes of gases consumed/produced in a reaction using gas stoichiometry.

• Non-Ionic Reactions

  • With few exceptions, the multitude of reactions discussed in this and other introductory texts are classified as ionic reactions.
  • Here we shall consider two other classes of organic reactions: Free-Radical Reactions & Pericyclic Reactions.
  • One type of "free-radical reaction", alkane halogenation has already been described.
  • In contrast to ionic reactions, both free radical and pericyclic reactions may occur in the gas phase, as well as in solution in various solvents.
  • Also, these nonionic reactions are more tolerant of spectator functional groups than are many ionic reactions.

• Irreversible Addition Reactions

  • Lithium aluminum hydride is by far the most reactive of the two compounds, reacting violently with water, alcohols and other acidic groups with the evolution of hydrogen gas.
  • Before leaving this topic it should be noted that diborane, B2H6, a gas that was used in ether solution to prepare alkyl boranes from alkenes, also reduces many carbonyl groups.
  • Consequently, selective reactions with substrates having both functional groups may not be possible.
  • Because of their ring strain, epoxides undergo many carbonyl-like reactions, as noted previously.
  • A common pattern, shown in the shaded box at the top, is observed in all these reactions.

• Measuring Reaction Rates

  • The volume of oxygen produced can be measured using the gas syringe method.
  • The gas collects in the syringe, pushing out against the plunger.
  • The rate of a reaction that produces a gas can also be measured by calculating the mass loss as the gas forms and escapes from the reaction flask.
  • Note that it is not possible to collect the SO2 gas that is produced in the reaction because it is highly soluble in water.
  • In a reaction that produces a gas, the volume of the gas produced can be measured using the gas syringe method.

• Avogadro's Law: Volume and Amount

  • For example, 1.00 L of N2 gas and 1.00 L of Cl2 gas contain the same number of molecules at Standard Temperature and Pressure (STP).
  • V is the volume of the gas, n is the number of moles of the gas, and k is a proportionality constant.
  • However, when chemists found that an assumed reaction of H + Cl $\rightarrow$ HCl yielded twice the volume of HCl, they realized hydrogen and chlorine were diatomic molecules.
  • The chemists revised their reaction equation to be H2 + Cl2 $\rightarrow$ 2HCl.
  • This discovery led to the correct molecular formula for water (H2O) and the correct reaction $2H_2O \rightarrow 2H_2 + O_2$.