Mass-Volume and Volume-Mass Stoichiometry - Chemistry LibreTexts
Formulas are about relationships between numbers. Mass and volume relate to each other through a concept called density. Density is how. The average kinetic energy of gaseous molecules is directly proportional to the absolute temperature of the kinenbicounter.info average kinetic. Calculate volumes of gases consumed/produced in a reaction using gas in volume or mass, of gas consumed or produced in a chemical reaction. relationships of the reactants and products in chemical reactions (chemical equations).
However, the first two steps of the problem remain unchanged. This is because the first step requires converting mass to moles.
Volume Relationships in Chemical Reactions
The second step involves a mol-mol ratio, once again pressure and temperature are immaterial. The final step involves calculating a volume of gas. It is at this point that the ideal gas law is used. After these first two steps, the following can be determined: The variable P represents pressure, and must be in atm.
The variable V is the volume, and is what we are solving for. The variable n represents moles, and 0. The variable R is the gas law constant and has a value of 0. It is for this reason that pressure must be in atmospheres. The temperature T must be in kelvin. First, let's make the necessary conversions for temperature and pressure.
For temperature, to convert degrees Celsius to kelvin, add Solving the above proportion gives a value of 1. Problems - Volume of Liquids On occasion, a liquid reactant may be used and the mass is not given.
Instead, the volume of the liquid is given as the starting quantity. Be careful with this as If lucky, the density of the liquid will be given in the problem. If not, then it must be found in literature. Using the density formula, the mass of the substance can be found mass equals volume multiplied by density and from there, the moles of the substance can be found. When included on the products side, the reaction is exothermic.
If included on the reactants side, the reaction in endothermic.
Either way, a mole-enthalpy ratio can be generated to determine a relationship between enthalpy, mass, volume, or any other stoichiometric quantity. Consider the exothermic reaction shown below: Consider the following question: What mass of europium will yield kJ of heat? Unlike previous stoichiometry problems that required three steps to solve, this one will only need two.
This is because the step that integrates a mole-mole ratio will be replaced with a mole-enthalpy ratio. This allows for a unit conversion moles to kilojoules and a stoichiometric ratio based on the reaction equation to be completed in one step. Problems - Limiting Reactant In the previous example, it was assumed that there was an unlimited supply of carbon monoxide to react with all of the iron. Sometimes this is not an appropriate or plausible assumption.
Sometimes two distinct masses of reactants are given, and it cannot be assumed that they will consume each other completely. Imagine trying to bake a cake.
Mass-Volume Relationships in Reactions Involving Gases by Luis Caldera on Prezi
The recipe states that two eggs are needed to make a cake. With a dozen eggs available, six cakes can be made. What if the recipe also states that a cup of sugar is necessary and only four cups of sugar are available? Regardless of the dozen eggs, only four cakes can be made, because after consuming four cups of sugar with eight eggsthere will be no sugar remaining.
At this point, no more cakes can be made. Sugar is considered the limiting reactant in this example. The eggs are the excess reactant.
Recall the reaction from before: What mass of iron will be produced from The solution is similar to the mass-mass problem from before, except there are two problems being solved at the same time. The reactant that produces the smaller mass or volume for a gas of product is the limiting reactant. Problems - Excess Reactant In the last problem it was imperative for us to calculate which reactant was consumed first because the reaction would stop at that point.
12.6: Mass-Volume and Volume-Mass Stoichiometry
The mass of products had to be determined from this substance, which was called the limiting reactant Fe2O3. The other substance that was not fully consumed CO is the excess reactant. The mass of carbon monoxide that is consumed can be calculated, and the mass of carbon dioxide that remains unreacted can also be found.
In order to do so, a stoichiometry problem must first be completed in which the limiting reactant is used to calculate the mass of excess reactant consumed. Solution Stoichiometry A solution stoichiometry problem will involve aqueous reactants for which you will need to calculate a molarity or volume.
Calculations that are part of a titration experiment are guaranteed to be solution stoichiometry. First, let's look at a solution stoichiometry problem that also incorporates some concepts discussed earlier on this page: Given the reaction that follows, find the volume of sulfur dioxide gas that will be produced from This problem is unique in that there are two numbers given within the problem, but since they are not values for different compounds, it is not a limiting reactant problem.
The volume and molarity given must be used to find the number of moles of HCl. From there, the rest of the problem continues in the same manner as previous problems. Another problem appears when we weigh the gases: If we assume that these volumes contain equal numbers of particles, then we must conclude that 1 oxygen particle weighs more than 1 water particle.
It would seem that a water molecule, which contains at least one oxygen atom, should weigh more than a single oxygen particle. These are serious objections to the idea that equal volumes of gas contain equal numbers of particles. Our postulate appears to have contradicted common sense and experimental observation. However, the simple ratios of the Law of Combining Volumes are also equally compelling. Why should volumes react in simple whole number ratios if they do not represent equal numbers of particles?
Consider the opposite viewpoint: Now when we combine particles in simple whole number ratios to form molecules, the volumes of gases required would produce decidedly non-whole number ratios. The Law of Combining Volumes should not be contradicted lightly. There is only one logical way out. We will accept our deduction from the Law of Combining Volumes that equal volumes of gas contain equal numbers of particles, a conclusion known as Avogadro's Hypothesis.
How do we account for the fact that 1 liter of hydrogen plus 1 liter of chlorine yields 2 liters of hydrogen chloride?
Volume Relationships in Chemical Reactions
There is only one way for a single hydrogen particle to produce 2 identical hydrogen chloride molecules: In fact, each hydrogen particle or molecule must contain an even number of hydrogen atoms. Similarly, a chlorine molecule must contain an even number of chlorine atoms.
We will assume the simplest possibility and see if that produces any contradictions.
This is a wonderful result, for it correctly accounts for the Law of Combining Volumes and eliminates our concerns about creating new atoms. Most importantly, we now know the molecular formula of hydrogen chloride. We have, in effect, found a way of "counting" the atoms in the reaction by measuring the volume of gases which react.Mole Ratio Practice Problems
This method works to tell us the molecular formula of many compounds. Recall that the mass ratio in water is 8: Since there are two hydrogen atoms for every oxygen atom in water, then the mass ratio requires that a single oxygen atom weigh 16 times the mass of a hydrogen atom.
To determine a mass scale for atoms, we simply need to choose a standard. For example, for our purposes here, we will say that a hydrogen atom has a mass of 1 on the atomic mass scale. Then an oxygen atom has a mass of 16 on this scale. Our conclusions account for the apparent problems with the masses of reacting gases, specifically, that oxygen gas weighs more than water vapor.