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Chemistry 141 Exam -2 Questions & 100% Verified Correct Answers with complete solutions (Latest update

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Chemistry 141 Exam -2 Questions & 100% Verified Correct Answers with complete solutions (Latest update

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  • August 15, 2024
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Chemistry 141 Exam #2
The relationship between the macroscopic and molecular level.

Allows us to calculate how much "stuff" can be produced in a reaction...

...or the relationship between any two components in a reaction. - ANS-What is stoichiometry?

In the "real world" we don't deal with isolated molecules or atoms (they are too small to weigh).

We use the mole to allow us to connect the molecular level to the observable macroscopic level.
- ANS-What does the mole allows us to do?

• Just a number! - A big number...
• 6.022 x 1023 "things" - ANS-What is a mole?

B. ~ 10^14 - ANS-• If 1 planet can hold maximum 6 x 109 people, how many planets would you
need to hold 1 mole of people?
A. ~ 10^18
B. ~ 10^14
C. ~ 10^32
D. ~ 10^2.5

formula mass in grams - ANS-What is the mass of 1 mole of any substance equal to?

mass in grams of 1 mole - ANS-What is molar mass?

02: 32g/mol

NaOH: 40g/mol

UF6: 352 g/mol - ANS-What is the molar mass of 02, NaOH, and UF6?

Mass is conserved and atoms are rearranged. - ANS-How is mass handled in chemical
reaction?

2 C6H14 + 19O2 --> 12 CO2 + 14 H2O - ANS-Balance the following equation:
__C6H14 + __O2 --> __CO2 + __H2O

1. Start with an element that is only in one substance on the reactant and product side.

2. Do it again if you can.

,3. Then see how many of the remaining elements you need and balance.

4. check to make sure each side has the same # of atoms. - ANS-How do you balance
equations?

2N2 + O2 ----> 2N2O - ANS-__N2 + __O2 ----> __N2O
Balance the equation
Draw out the balanced equation.
What is the best representation of the products?

__FeCl3 + 3NaOH----->__Fe(OH)3 + 3NaCl - ANS-Balance the following equation: __FeCl3 +
__NaOH------>__Fe(OH)3 + __NaCl

1.98 mole Ca(NO3) - ANS-How many moles of calcium nitrate (Ca(NO3)2) are in 325g?

One Mole Ca
Two Moles N
12 Moles O - ANS-How many moles of O atoms, Ca atoms, N atoms are in 2 mole Ca(NO3)2 ?

E. They all have the same number. - ANS-Which of the following contains the largest number of
molecules?
A. 1 mol CH4 B. 1 mol C2H6
C. 1 mol SO2
D. 1 mol CCl4
E. They all have the same number

B. 1 mol C2H6 (8 atoms) - ANS-Which one has the largest # of atoms?
A. 1 mol CH4
B. 1 mol C2H6
C. 1 mol SO2
D. 1 mol CCl4
E. They all have the same number

Compare the molar masses and see which one is the smallest.
A. 10.0 g CH4

Analogy: 1 lb of m&m and 1 lb of snickers. - ANS-Which of the following contains the largest
number of molecules?
A. 10.0 g CH4
B. 10.0 g C2H6
C. 10.0 g SO2
D. 10.0 g CCl4
E. They all have the same number

,We cannot use mass-mass ratios when we do stoichiometric calculations!
We must convert to moles - ANS-Can we use mass-mass ratios when you do stoichiometric
calculations?

Must use mass to mole conversion factors or vice versa (g/mol or mol/g) - ANS-What do you
use to convert from mass to
moles or from moles to mass?

Use mass/mole conversions to compare and predict amounts of products and/or reactants in
reactions - ANS-What is reaction stoichiometry?

- ANS-What does the stoichiometry map look like?

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
5. Reflect on answer - ANS-Whats the general procedure for stoichiometry?

3H2 + N2 ---> 2NH3

4mol NH3 - ANS-How many moles of NH3 would be produced if 6 moles of H2 reacted with
excess N2?

N2 + 3H2 -> 2NH3
38.5gramsN2 - ANS-How many grams of N2 would be required to produce 2.75 moles of NH3?

Amount of one of the reagents,
which limits how much product can be formed - ANS-Describe a limiting reactant problem

C2H4O will be the limiting reactant. 2 H20 will be leftover. - ANS-If you have 5 H20 and 3
C2H4O, what will be the limiting reactant in the equation: C2H4O + H20--> C2H6O2

How much H2O will be left over?

Calculate the amount of product possible from each reactant. The smallest amount must be
from limiting reactant. - ANS-How do you calculate a limiting reactant?

4 mol NH3 will be produced.

H2 is the limiting reactant because it limits how much of NH3 can be produced.

, The remaining amount will be 1 mol N2 - ANS-How many moles of NH3 would be produced if 6
moles of H2 reacted with 3 moles of N2?

How much NH3 will be produced?

Which is the limiting reactant?

How many moles of N2 remain at the end?

Remaining amount = starting amount - amount used - ANS-How do you calculate the remaining
amount of the excess reactant in a limiting reactant problem?

B. O2 - ANS-The equation for a reaction is 2 S + 3 O2--->2 SO3.

You have 6 S and 3 O2.

Which is the limiting reactant?
A.S
B. O2
C. SO3
D.There is no limiting reactant

4 SO3 and 2 S - ANS-The equation for a reaction is 2 S + 3 O2--->2 SO3.

You have 6 S and 3 O2.

What will the product mixture have in it?

27.5g CO2 - ANS-How many grams of carbon dioxide would be produced if 10 g of methane are
combusted in excess oxygen?

1. B) O2

2. B. 72% - ANS-If you had 10g of methane and 10g of oxygen, what is the maximum mass
(grams) of carbon dioxide that could be produced?
CH4 + 2O2 ----> CO2 + 2H2O


Which is the limiting reactant?
A) CH4
B) O2
C) CO2
D)There is no limiting reactant
E) I don't know

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