Module 5 review

For the following formula, classify the reaction as formation, decomposition, combustion, or none of these.

 

2HgO(s)  →    2Hg(l)  +  O2(g)

Decomposition

 

A decomposition reaction is the opposite of a synthesis reaction – a complex molecule breaks down to make simpler ones. These reactions come in the general form:

For the following formula, classify the reaction as formation, decomposition, combustion, or none of these.

 

 

8 Fe + S8 —> 8 FeS

Formation

 

A reaction that starts with 2 or more elements and produces one compound

For the following formula, classify the reaction as formation, decomposition, combustion, or none of these.

 

2FeCl (s) + Br (g) ——> BrCl4 (ag)  + 2Fe

None of these

For the following formula, classify the reaction as formation, decomposition, combustion, or none of these.

 

C10H8 + 12 O2 —> 10 CO2 + 4 H2O

Combustion:

 

 A combustion reaction is when oxygen combines with another compound to form water and carbon dioxide. These reactions are exothermic, meaning they produce heat. An example of this kind of reaction is the burning of napthalene:

Write the chemical equation for the formation of

 

CaCO3

A. Ca + C + O—–> CaCO3

this is not balanced yet

 

 

B. 2Ca + 2C + 3O—–> 2CaCO3

now it is balanced

Write the chemical equation for the decomposition of:

 

PbSO4

A. PbSO4  —–> Pb + S + O2

not balanced yet

 

B. 2PbSO4 —–> 2Pb + 2S + 4O2

now it is balnced and broken down into its constituents

 

 

Write the chemical equation for the complete combustion of

 

CH4(g) + 2O2(g)

CH4(g) + 2O2(g) —-> 2H2O(g) + CO2(g)

What is the mass of a calcium atom in kg?

 

40.1amu  x  1.66 x 10-24g   x    1kg             

    1             1 amu             1,000g     =       

What is the mass of an C4H6O2 molecule in amu?

 

 

 C= 12 x 4 = 48

H=1.01 x 6 = 6.06

O=16 x 2= 32

 

48+6.06+32 =86.06

 

86.06 amu is the answer

How many moles are in  24.2g of C4H6O2

 

We already know there is 86.06 amu from the previous card.

 

This means 1 mole is equal to 86.06grams. Now we can use this in a conversion:

 

24.2g  x   1mole  

   1         86.06g    =   0.2812 moles

 

If a chemist has 10.5 moles of C4H6O2,what is the mass of the sample?

 

 

Again, we know there is 86.06 amu

 

This means 1 mole = 86.06. Now we can convert from moles to grams

 

10.5moles86.06g 

     1            1 mole   = 903.63g is the answer

 

If a chemist has .025moles of Ca2CO and causes it to decompress into its constitent elements, how many moles of oxygen will form?

First we need to figure out the decompression reaction:

Ca2CO3   —–> Ca + C + O2

This is not balanced, so lets balance the equation:

 

2Ca2CO3   —–> 2Ca + 2C + 3O2 (now its Balanced)

 

Thus 2 moles of Ca2CO= 3 moles of O2

 

So now we can figure it out:

 

 .025 moles of Ca2CO3   x   3 moles O

               1                              2 moles of Ca2CO3 

 

 

= 0.375 moles of O2

Which sample has more atoms in it:

12 grams of Copper (Cu) or 15 grams of Potassim (K)

 

 

To count atoms, we need to know how many moles. Thus, we need to take these masses and convert them to moles

 

12gCu  x 1 mole Cu 

   1         63.5gCu       = 0.189 moles of Cu

 

 

15gK   x  1 mole K       

   1         39.1gK        =  0.383 moles of K

 

 

Thus 15g of Potassum has more atoms than 12 grams of Copper.

Your fireplace has poor ventilation. What should you be concerned about?
You should be worried about incomplete combustion which could produce carbon monoxide, a poisonous gas.
A chemist has one more of an unknown molecule. The mass of this sample is 48.3 grams. After doing some tests, the chemist discovers there are 2 molecules of carbon and one other substance that cannot be identified. In other words, the molecule’s formula is XC2 where “X” is unknown. Based on the mass of this;sample, what is atom “X”?

Since we have one mole, the mass of the sample in grams is also the mass of the molecule in amu. Thus, we know that this molecule mass is 48.3 am. Since it has 2 molecules of carbon, the carbon atoms take up 24 amu of that mass. Thus, 24.3 amu are left for “X”. If you look at periodic chart. the only atom with a mass;24.3;is Magnesium (Mg).

;

So “X”;is Magnesium;

The mole is ___________’s number
Avogardo
Avogardo’s number is equal to:
6.02 x 1023
x

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