Mass and Energy Balances
Using a balanced chemical equation to calculate amounts of reactants and products is You might see this ratio called the mole ratio, the stoichiometric factor, or the stoichiometric ratio. . Example: Using mole ratios to calculate mass of a reactant .. To get ADP in and at the same time ATP out of the matrix there is the. In balancing chemical equations, the coefficients are related to the moles of balanced equations is central in determining mass relationships in chemical reactions liter (mol/L) disappearing per unit time (or some quantity related to molarity. Unit Conversion · Periodic Table of Elements · Time Reference & Exact Time where E is the energy of the object in question, m0 is its rest mass, c is the where v is the object's velocity. This relationship can probably be found in most introductory college physics texts. . Ultimate Chemistry Set CHEM C v $
A chemical reaction is the process by which substances bond together or break bonds and, in doing so, either release or consume energy see our Chemical Reactions module. A chemical equation is shorthand that scientists use to describe a chemical reaction. Let's take the reaction of hydrogen with oxygen to form water as an example. If we had a container of hydrogen gas and burned this in the presence of oxygen, the two gases would react together, releasing energy, to form water.
To write the chemical equation for this reaction, we would place the substances reacting the reactants on the left side of an equation with an arrow pointing to the substances being formed on the right side of the equation the products. Given this information, one might guess that the equation for this reaction is written: Unfortunately, there are two problems with this chemical equation. First, because atoms like to have full valence shells, single H or O atoms are rare.
In nature, both hydrogen and oxygen are found as diatomic moleculesH2 and O2, respectively in forming diatomic molecules the atoms share electrons and complete their valence shells. Hydrogen gastherefore, consists of H2 molecules; oxygen gas consists of O2. Correcting our equation we get: As written, this equation tells us that one hydrogen molecule with two H atoms reacts with one oxygen molecule two O atoms to form one water molecule with two H atoms and one O atom.
In other words, we seem to have lost one O atom along the way! Balancing equations To write a chemical equation correctly, the number of atoms on the left side of a chemical equation has to be precisely balanced with the atoms on the right side of the equation.
If we have atoms of each element, the ratio of the masses is approximately 1, As long as we have equal numbers of hydrogen and oxygen atoms, the ratio of the masses will always be The same consistency is seen when ratios of the masses of other elements are compared.
For example, the ratio of the masses of silicon atoms to equal numbers of hydrogen atoms is always approximately So we have established that the masses of atoms are constant with respect to each other, as long as we have the same number of each type of atom. Consider a more macroscopic example. If a sample contains 40 g of Ca, this sample has the same number of atoms as there are in a sample of 7 g of Li. What we need, then, is a number that represents a convenient quantity of atoms so we can relate macroscopic quantities of substances.
Clearly even 12 atoms are too few because atoms themselves are so small. We need a number that represents billions and billions of atoms.
Mass–energy equivalence - Wikipedia
A mole is defined as 6. Just as a dozen implies 12 things, a mole abbreviated mol represents 6. Thus, if we have 6. Similarly, if we have 0. Notice that we are applying the mole unit to different types of chemical entities. In these examples, we cited moles of atoms and moles of molecules. The word mole represents a number of things—6.
They can be atoms, formula units of ionic compoundsor molecules. That information still needs to be specified.
Because 1 H2 molecule contains 2 H atoms, 1 mol of H2 molecules 6. Using formulas to indicate how many atoms of each element we have in a substance, we can relate the number of moles of molecules to the number of moles of atoms. For example, in 1 mol of ethanol C2H6Owe can construct the following relationships Table 6.
Molecular Relationships Back to the Top 6. Atomic and Molar Mass Now that we have introduced the mole and practiced using it as a conversion factor, we ask the obvious question: Why is it 6. Whereas one hydrogen atom has a mass of approximately 1 amu, 1 mol of H atoms has a mass of approximately 1 gram.
And whereas one sodium atom has an approximate mass of 23 amu, 1 mol of Na atoms has an approximate mass of 23 grams.
One mole of a substance has the same mass in grams that one atom or molecule has in atomic mass units. This is because all atoms are made up of the same parts protons, neutrons, and electrons with the protons and neutrons having nearly identical masses. Electrons, since they are so light, are negligent in their contribution to atomic mass, even in the largest atoms. Thus, an important three way relationship is formed: This effectively gives us a way to count molecules in the laboratory using a common balance!
Note that in chemical equations and calculations that mole concentrations are abbreviated as mol. Recall that, the mass of an ionic compound referred to as the formula mass or a covalent molecule referred to as the molecular mass —is simply the sum of the masses of its atoms.
To calculate formula or molecular masses, it is important that you keep track of the number of atoms of each element in the molecular formula to obtain the correct molecular mass. The mole concept can be extended to masses of formula units and molecules as well. The mass of 1 mol of molecules or formula units in grams is numerically equivalent to the mass of one molecule or formula unit in atomic mass units.
For example, a single molecule of O2 has a mass of As with atomic mass unit—based masses, to obtain the mass of 1 mol of a substance, we simply sum the masses of the individual atoms in the formula of that substance.
The mass of 1 mol of a substance is referred to as its molar masswhether the substance is an element, an ionic compound, or a covalent compound.