How did they find -4.895E+6 J? What does the E +6 mean? Does that mean raise to

Question

How did they find -4.895E+6 J? What does the E +6 mean? Does that mean raise to a power? Please answer clearly.

The molar heat of combustion of 1,8-octanediol is the energy released when one mole of this compound is burned:

It is useful to table the data for calorimetery questions:

The heat given off by the reaction is equal to the heat gained by the water + calorimeter.  

In this case you must determine qcal from qwater and qrxn:  

1. Calculate the heat absorbed by the water:

2. Calculate the heat evolved by the combustion of 0.478 grams of C8H18O2.  Molar mass= 146.23 g/mol:

3. Calculate the heat absorbed by the calorimeter:

4. Calculate the heat capacity of the calorimeter:

C8H18O2(s) + (23/2) O2(g) 9 H2O(l) + 8 CO2(g) + Energy

The heat given off by the reaction is equal to the heat gained by the water + calorimeter.  
?qrxn = qwater +  qcal
It is useful to table the data for calorimetery questions:

       Water        Calorimeter        Sample mass
1195 g H2O


0.549 g C8H18O2 C
4.184 J/goC
890.4 J/oC

Tfinal  
28.48oC
28.48oC

Tinitial  
25.36oC
25.36oC

T  
3.12o
3.12o

q  
mwaterCwaterT
CcalT
?(qwater + qcal)


Molar Heat of Combustion = ?

Notice since this is a chemical reaction, you cannot calculate qrxn from mass and specific heat.  You must use qwater and qcal.

1. Calculate the heat gained by the water:
qwater =    1195 g H2O 4.184 J      3.12oC    =   15600 J goC

2. Calculate the heat gained by the calorimeter:
qcal =    890.4 J 3.12oC    =   2778 J oC

3. Calculate the heat given off by the reaction:
qrxn = ?(qwater +  qcal) = ?(15600 J + 2778 J) = ?18378 J

4. Calculate the heat of reaction per gram of 1,8-octanediol:
qrxn    =   ? 18378 J    =   -33475 J/g gram 0.549 g

5. Calculate the heat of reaction per mole using the molecular weight of 1,8-octanediol (C8H18O2, Molar mass = 146.23 g/mol)

-33475 J         146.23 g C8H18O2    =    -4.895E+6 J    g C8H18O2 mol C8H18O2 mol C8H18O2

6.  Finally, convert J to kJ.
Molar Heat of Combustion =   -4.895E+6 J       1 kJ    =   -4895 kJ   mol C8H18O2 1000 J mol C8H18O2









-33475 J         146.23 g C8H18O2    =    -4.895E+6 J    g C8H18O2 mol C8H18O2 mol C8H18O2 C8H18O2(s) + (23/2) O2(g) rightarrow 9 H2O(l) + 8 CO2(g) + Energy The heat given off by the reaction is equal to the heat gained by the water + calorimeter. ?qrxn = qwater + qcal

Explanation / Answer

2)

it is obtained by 33475 x 146.23 = 4895049.25

Given -4.895E+6

it is basically used for very small or large numbers eg in excel when there isnt space to write them.

You just move the decimal place however many spaces - in this case it is + 06 so 6 to the left

So -4.895E+6 = -4895049.25

2) -(-1.665E+4 J + 1.420E+4 J)

Here E+4 is nothing but 10^4

So -(-1.665E+4 J + 1.420E+4 J) = - ( -1.665 x 10^4 + 1.420 x 10^4 )

-(-1.665E+4 J + 1.420E+4 J) = 2450 J

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