1 | Page
Michigan State University
CEM 141 CEM 141 EXAM 2 Questions and
Answers 2026 Latest Update
Stoichiometry Ans: The relationship between the macroscopic and
molecular level
Stoichiometry allows us to.... Ans: calculate how much "stuff" can be
produced in a reaction
or the relationship b/w any two components in a reaction
We use the mole to.... Ans: allow us to connect from the molecular level to
the observable macroscopic level
In the real world, we don't deal with isolated molecules (any anyway they are
too small to weigh)
Avogadro's number Ans: 6.022x10^23 "things" (this is called Avogadro's
number)
It is defines as the number of carbon atoms in 12 g of C-12 (isotope of C
with 6 protons and 6 neutrons)
The mole and chemistry Ans: Still just a number (a big number)
6.022x10^23 "things" (this is called Avogadro's number)
It is defines as the number of carbon atoms in 12 g of C-12 (isotope of C
with 6 protons and 6 neutrons)
The mass of 1 mole of any substance = formula mass in grams
E.g. mass of 1 mole of water (h2o) = 18 grams
What is the concept of a mole and what is it used for? Ans: Translation b/w
molecular and macroscopic scale
© 2026 All rights reserved
, 2 | Page
General procedure for stoicheiometry Ans: 1. Write a balanced equation
2. Draw a map of where you are starting and how you will get to the end
3. Write out the calculation with units!
4. Calculate
Molar mass Ans: mass of 1 mole in grams
Significant Figures Ans: More important when you're working in the lab than
in a lecture class
On tests, we would like you to be close to having the correct number of sig
figs but will not penalize you for being off by one sig fig. We are most
interested in seeing that you can set up solutions to problems correctly.
Stoichiometry 2 Ans: Use mass/mole conversions to compare and predict
amounts of products and/or reactants in reactions
Limiting Reagents Ans: Amount of one of the reagent (reactants) limits how
much product can be formed
To calculate limiting reactant Ans: Do not compare masses directly
Pick one product and calculate the amount of this product possible from
each reactant
Whichever produces the least product is the limiting reactant (the amount
can be moles or grams of the product selected, whichever is most
convenient unless specified)
Percent yield example Ans: (given amount / your calculation) x100%
How does the existence of atoms explain the conservation of matter? Ans:
The Conservation of Matter states that matter cannot be created or
destroyed and with the existence of atoms we see this to be true because
these atoms react with one another and create a balanced outcome of a
product from the reactants.
Why do we use moles when we try to determine amounts of reactants and
products in a reaction? Ans: We need to use moles because molecules are so
© 2026 All rights reserved
Michigan State University
CEM 141 CEM 141 EXAM 2 Questions and
Answers 2026 Latest Update
Stoichiometry Ans: The relationship between the macroscopic and
molecular level
Stoichiometry allows us to.... Ans: calculate how much "stuff" can be
produced in a reaction
or the relationship b/w any two components in a reaction
We use the mole to.... Ans: allow us to connect from the molecular level to
the observable macroscopic level
In the real world, we don't deal with isolated molecules (any anyway they are
too small to weigh)
Avogadro's number Ans: 6.022x10^23 "things" (this is called Avogadro's
number)
It is defines as the number of carbon atoms in 12 g of C-12 (isotope of C
with 6 protons and 6 neutrons)
The mole and chemistry Ans: Still just a number (a big number)
6.022x10^23 "things" (this is called Avogadro's number)
It is defines as the number of carbon atoms in 12 g of C-12 (isotope of C
with 6 protons and 6 neutrons)
The mass of 1 mole of any substance = formula mass in grams
E.g. mass of 1 mole of water (h2o) = 18 grams
What is the concept of a mole and what is it used for? Ans: Translation b/w
molecular and macroscopic scale
© 2026 All rights reserved
, 2 | Page
General procedure for stoicheiometry Ans: 1. Write a balanced equation
2. Draw a map of where you are starting and how you will get to the end
3. Write out the calculation with units!
4. Calculate
Molar mass Ans: mass of 1 mole in grams
Significant Figures Ans: More important when you're working in the lab than
in a lecture class
On tests, we would like you to be close to having the correct number of sig
figs but will not penalize you for being off by one sig fig. We are most
interested in seeing that you can set up solutions to problems correctly.
Stoichiometry 2 Ans: Use mass/mole conversions to compare and predict
amounts of products and/or reactants in reactions
Limiting Reagents Ans: Amount of one of the reagent (reactants) limits how
much product can be formed
To calculate limiting reactant Ans: Do not compare masses directly
Pick one product and calculate the amount of this product possible from
each reactant
Whichever produces the least product is the limiting reactant (the amount
can be moles or grams of the product selected, whichever is most
convenient unless specified)
Percent yield example Ans: (given amount / your calculation) x100%
How does the existence of atoms explain the conservation of matter? Ans:
The Conservation of Matter states that matter cannot be created or
destroyed and with the existence of atoms we see this to be true because
these atoms react with one another and create a balanced outcome of a
product from the reactants.
Why do we use moles when we try to determine amounts of reactants and
products in a reaction? Ans: We need to use moles because molecules are so
© 2026 All rights reserved
