Chemistry 2 UNIT 5 STOCHIOMETRY
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86 Terms
What is a measurement?
A quantity that has both a number and a unit.
How many hydrogen atoms are in 1 gram of hydrogen?
6.02 × 10^23 atoms.
Express Avogadro's number in scientific notation.
6.02 × 10^23
True or False: The coefficient in scientific notation must be between 1 and 10.
True
What type of exponent do very large numbers have in scientific notation?
Positive
What type of exponent do very small numbers have in scientific notation?
Negative
How is accuracy evaluated?
By comparing a measurement to a known or accepted value.
How is precision evaluated?
By comparing multiple measurements to each other.
True or False: Experimental values are always the same as accepted values.
False
What is error?
The difference between accepted and experimental values.
What is the percent error formula?
Percent Error = |Experimental − Actual| / Actual × 100
True or False: With a thermometer marked every 1°C, you can estimate to the nearest 0.1°C.
True
What do significant figures communicate?
The precision of a measurement.
True or False: Nonzero digits are always significant.
True
Are zeros always significant?
No, they may or may not be significant.
Are all digits for measurement in scientific notation significant?
Yes
What does a mole measure?
The amount of matter.
What are different ways to measure matter?
Mass, volume, and counting particles.
How are units converted from one form to another?
Using conversion factors.
In a conversion factor, which unit goes on top?
The desired unit.
In a conversion factor, which unit goes on the bottom?
The given unit.
What is a mole?
The official counting unit of chemistry.
What is Avogadro's number?
6.02 × 10^23
What is the relationship between a mole and Avogadro's number?
1 mole = 6.02 × 10^23 particles.
What are the representative particles of molecular compounds?
Molecules.
What are the representative particles of ionic compounds?
Formula units.
What are the representative particles of elements?
Atoms.
What is the representative particle for carbon?
Atom.
What is the representative particle for water?
Molecule.
What is the representative particle for sodium chloride?
Formula unit.
How many representative particles are in 1 mole of any substance?
6.02 × 10^23 particles.
How do you convert moles to particles?
Multiply by Avogadro's number.
How do you convert particles to moles?
Divide by Avogadro's number.
Atomic mass units (amu) are based on what element?
Carbon-12.
True or False: Masses on the periodic table represent two different measurements.
True.
The mass on the periodic table is atomic mass in what units?
amu.
The mass on the periodic table is also molar mass in what units?
g/mol.
What is needed to calculate the molar mass of a compound?
A chemical formula.
How do you calculate molar mass?
Multiply each subscript by the element's molar mass and add the totals.
What is molar mass?
The mass in grams of 1 mole of a substance.
As what particles increase on the periodic table, molar mass generally increases?
Protons and neutrons.
Can moles be measured directly in the lab?
No.
What measurement is usually taken directly in the lab instead of moles?
Mass.
What units are commonly used to measure mass in chemistry?
Grams.
Why do scientists convert measurements to moles?
Moles can be used in stoichiometric calculations.
How do you convert grams to moles?
Divide by molar mass.
How do you convert moles to grams?
Multiply by molar mass.
True or False: A mole of any substance is an extremely large amount.
True.
What measurements are involved in a chemical reaction?
Moles, mass, particles, and volume relationships.
In a chemical reaction, existing substances are changed into what?
New substances.
What adjusts the amount of product formed in a balanced equation?
The coefficients.
What is calculating quantities using a balanced equation called?
Stoichiometry.
SKIP——>
What information can be obtained from a balanced equation?
Mass, volume of gas,number of molecule, and number and type of ions
True or False: Subscripts are useful for comparing substances in a chemical equation.
False.
Why are moles the most useful information from balanced equations?
They can be converted into many other measurements.
What is always conserved in a chemical reaction?
Mass and atoms
Why are balanced chemical equations essential for stoichiometry?
They provide mole ratios.
Where do mole ratios come from?
The coefficients of a balanced equation.
What are mole ratios used to convert between?
Different substances.
When setting up a mole ratio, which substance goes on top?
The unknown.
When setting up a mole ratio, which substance goes on the bottom?
The given.
In mass-to-mass stoichiometry, the amount of a solid is usually measured by what?
Mass.
Most practical stoichiometry problems require how many steps?
Three.
What is the first step of mass-to-mass stoichiometry?
Convert grams of given substance to moles.
What is the second step of mass-to-mass stoichiometry?
Use a mole ratio.
What is the third step of mass-to-mass stoichiometry?
Convert moles to grams of the unknown substance.
Besides mass, what other units can be used in stoichiometry?
Volume, particles, and concentration.
What conversion factor is used for particles?
Avogadro's number (6.02 × 10^23).
What conversion factor is used for gas volume at STP?
22.4 L/mol.
What is a limiting reagent?
The reactant that is used up first and stops the reaction.
What is an excess reagent?
A reactant that remains after the reaction is complete.
True or False: A reaction stops before the limiting reagent is used up.
False.
How do you determine the limiting reagent?
Convert all reactants to moles and compare.
What determines the amount of product formed?
The limiting reagent.
True or False: You must always determine the mass of the product formed.
False.
The reactant that forms less product is called what?
The limiting reagent.
True or False: The reactant with less mass always forms less product.
False.
What is theoretical yield?
The maximum amount of product possible from a given amount of reactant.
How is theoretical yield determined?
By stoichiometry calculations.
What is actual yield?
The amount of product actually recovered from a reaction.
Is actual yield usually greater than theoretical yield?
No.
What are chemists interested in maximizing?
Actual yield.
What does percent yield compare?
Actual yield to theoretical yield.
What is the percent yield formula?
Percent Yield = Actual Yield / Theoretical Yield × 100
What can decrease actual yield?
Impure reactants,Competing side reactions,Loss of product during recovery,Human error.