Answer: C. ethanol
The enthalpy of combustion is the amount of heat produced when one mole of ethanol undergoes complete combustion at 25 ° C and 1 atmosphere pressure, yielding products also at 25 ° C and 1 atm.
<u>The enthalpy of combustion of the unknown compound is</u>
ΔH = - 320 kJ / 0.25 mol = - 1280 kJ / mol
<u>To choose a probable compound according to this combustion enthalpy, we must evaluate the deviation in relation to the values reported in the literature for the three probable compounds</u> (methane, ethylene and ethanol). The deviation (e%) will be calculated according to the following equation,
e% = ( | ΔHx - ΔH | / ΔHx ) x 100%
where ΔHx is the enthalpy of combustion of the probable compound.
The following table shows the combustion enthalpies of the probable compounds and their deviation in relation to the enthalpy of ΔH = - 1280 kJ / mol
Compound Enthalpy of combustion (kJ/mol) Deviation
Methane - 890.7 43.8%
Ehylene -1411.2 9.3%
Ethanol -1368.6 6.5%
According to the previous table, we can say that the most probable compound is ethanol, since it has the smallest deviation in relation to the experimental enthalpy value of combustion.
5.6 atm
In a container, the sum of partial pressures equals the total pressure. If the sun is 9.8 atm and the partial pressure of oxygen is 4.2 atm, the rest of the gases must account for the other 5.6 atm.
This is a double replacement reaction. To balance the equation, you can not change the subscript because it will fully change the equation. Instead you change the coefficient infront of the element.
4 NaI + 1 Pb(SO4)2 —> 1 PbI4 +2 Na2SO4
The molality of the toluene is 1.46 mol/kg.
<h3>
What is molality?</h3>
The molality of a solution is its molal concentration. Molal concentration is denoted by m. It is the mol of solute dissolves in 1 Kg solvent.
The depression at freezing point is directly proportional to the molality of the solution. The equation we use for this type of problem is:
ΔT=iKm 
Where, ΔT
is depression at freezing point, i is Van't hoff factor, m is molality and
is the freezing point depression constant.
Toluene is a non-electrolyte and so the value of i for this is 1.
Depression at a freezing point is given as -13.
and the
is given as 5.12. So, we could calculate the molality of the solution using the equation written above.
Let's plug in the values in the equation:
ΔT=iKm
-7.51 =1 x5. 12 xm
m = 
m = 1.46 m
It means the molality of the solution is 1.46 mol/kg.
Hence, the molality of the solution is 1.46 mol/kg.
Learn more about the molality of the solution here:
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