Chapter 3 Flashcards
Define chemical Stoichiometry
Area of study where the quantities if materials consumed and produced in chemical reactions are considered
If you know the __ __ of objects, the objects behave as they were all __
Average mass; Identical
To count atoms, determine the # of __ in a sample by finding its __
Atoms; Mass
Modern system of atomic masses is based in __ as the standard
12C
__ is assigned a mass of exactly __ atomic mass units (amu)
12C; 12
Define mass spectrometer
An instrument used to determine the relative masses of atoms or the isotopic composition of a natural element by the deflection of their ions on a magnetic field
Accelerating ions produce own __ __, interacts with applied __ __, which tends to change the path of the __ (most massive __ are deflected the __ & separate)
Magnetic field; Magnetic field; Ion; Ions; Least
Masses of atoms are called __ __; atomic mass of _ is an average value of isotopes
Atomic weight; C
Define mole
Number equal to the number of carbon atoms in exactly 12 grams of pure 12C
Define average atomic mass
Average mass of an element
Define molar mass (molecular weight)
Mass in grams of one mole of the compound
Define Avogadro’a number
6.022 • 10^23; number of units of a substance in one mole of it
Mass of 1 mole of an element is equal to its __ __ in __; 6.022 • 10^23 __ = 1 _
Atomic mass; Grams; Amu; g
To find the molar mass, sum the masses of the __ __
Component atoms
2 common ways to describe the composition of atoms
of atomsPercentage of elements
Define mass percent (weight percent)
Percent by mass of a given element in a compound ((mass of element in 1 mole of compound / total mass of 1 mole of compound) x 100)
To determine the formula of a compound, most often a __ sample of the compound is either __ into its component elements or __ with oxygen to produce substances that are than __ and __
Weighed; Decomposed; Reacted; Collected; Weighed
Since the formula of a compound indicates the number of __ in the compound, masses of the elements must be converted to number of __ (easiest way is to use __ g)
Atoms; Atoms; 100.00
Numbers very close to whole numbers should be rounded to __ numbers for the integers
Whole
Define empirical formula
Simplest whole number ratio of atoms in a compound
Define molecular formula
Exact formula of a molecule, giving types of atoms and the number of each type
Molecular formula determination method 1 (4)
1) Obtain empirical formula2) compute the mass corresponding to the empirical formula 3) calculate the ratio (molar mass / empirical formula mass) 4) multiply the empirical formula by this integer to get the molecular formula
Empirical formula determination (4)
1) base calculations in 100g, each percent will then represent the mass in grams of that element2) determine number of moles of each element present in 100g of compound using atomic masses 3) divide each value of number of moles by the smallest values 4) multiply each number by an integer so the results are whole numbers
Define chemical equation
A representation of a chemical reaction showing the relative numbers of reactant and product molecules, and the nature of the reactants
Molecular formula determination method 2 (3)
1) Using mass %s and the molar mass, determine the mass of each element present in one mole of compound 2) determine the # of moles of each element present in one mole of compound 3) integers represent subscripts in the molecular formula
Define reactants
Starting substance in a chemical reaction; on left side of chemical equation
Chemical equations give the __ __ of the reactants and products
Physical states
Define products
Substance resulting from a chemical reaction; on right side of chemical equation
Define balancing a chemical equation
Making sure atoms are neither created not destroyed and all atoms present in the reactants must be accounted for among the products
Numbers if reactants & products are indicated by the __
Coefficients
Writing and balancing equations (3)
1) Determine reaction occurring (reactants, products, physical states) 2) write the unbalanced equation 3) balance the equation by starting with the most complicated molecules, determine coefficients necessary so the same number of each type of atom appears in both reactant and product sides, do not change formula of any compound
Define mole ratio
Ratio of moles of a substance to moles of another substance in balanced equations
Define haber process
The manufacture of ammonia from nitrogen & hydrogen, carried out at high pressure & high temperature with the aid of a catalyst
Calculating masses of reactants and products in chemical reactions (5)
1) balance equation2) convert known mass of reactant or product to moles of that substance 3) use balanced equation to set up mole ratios4) use mole ratios to calculate number of moles of desired reactant or product 5) convert from moles back to grams if necessary
Define Stoichiometric quantities
Quantities of reactants mixed in exactly the correct amounts so that all are used up at the same time
Always determine which reactant is __ to correctly calculate amounts of product form
Limiting
Define limiting reactant (limiting reagent)
Reactant that is completely consumed when a reaction is run to completion, and limits the amount of products that can be formed
Define theoretical yield
The maximum amount of a given product that can be formed when the limiting reactant is completely consumed
Define percent yield
Actual yield of a product as a percentage of the theoretical yield
Solving a Stoichiometry problem involving masses of reactants & products (5)
1) write & balance the equation for the reaction2) convert the known masses of substances to moles3) determine which reactant is limiting4) using the amount of the limiting reactant and the appropriate mole ratios, compute the number of moles of the desired product 5) convert from moles to grams, using the molar mass
Percent yield = (__ yield in g / __ yield in g) x 100%
Actual; Theoretical
Percent yield can indicate the __ of a particular __ or __ reaction
Efficiency; Laboratory; Industrial
