C.
-
10 cm3 of ethyl ethanoate was measured into an insulated beaker. Its temperature was recorded.
-
This was added to 10 cm3 of trichloromethane and was mixed well. The highest temperature attained was recorded.
D.
-
10 cm3 of ethyl ethanoate was measured into an insulated beaker. Its temperature was recorded.
-
This was added to 10 cm3 of trichloromethane and was mixed well. The highest temperature attained was recorded.
Result
Temperature change of solution
Calculation
B.
Mass of Ethanol: 0.81×(10×10-6)=0.0000081kg
Mass of Cyclohexane: 0.78×(20×10-6)=0.0000156kg
Total heat absorbed:
4×(0.0000081×2.44+0.0000156×1.83)
=0.000193248 kJ
mole of limiting reactant (i.e. ethanol):
0.0000081×1000/46=0.000176086 mole
The enthalpy change for one mole of ethanol that the hydrogen bond was broken is:
0.000193248/0.000176086
=1.09746 kJ/mole
D.
Mass of ethyl ethanoate: 0.9×(20×10-6)=0.000018kg
Mass of trichloromethane: 1.48×(10×10-6)=0.0000148kg
Total heat absorbed:
8×(0.000018×1.92+0.0000148×0.98)
=-0.000392512kJ
mole of limiting reactant (i.e. trichloromethane):
0.0000148×1000/119.5
=0.000123849mol.
The enthalpy change for one mole of trichloromethane that formed hydrogen bond is:
-0.000392512/0.000123849=-3.1693 kJ per mole
Conclusion
- The mixing process between ethanol and cyclohexane is endothermic.
- The enthalpy change for one mole of ethanol with hydrogen bond broken after mixed with Cyclohexane is 1.09746 kJ/mole.
- The mixing process between ethyl ethanoate and trichloromethane is exothermic.
- The enthalpy change for one mole of trichloromethane that formed hydrogen bond after mixed with ethyl ethanoate is -3.1693 kJ per mole
Discussion
A.
- The beaker should be insulated in order to prevent heat lost to surroundings.
- The temperature drops because there is hydrogen bonds between ethanol molecules and weaker van der waals’ force between cyclohexane molecules. The mixing of the two liquid break the hydrogen bonds. As bonds are broken, energy is needed. Therefore, heat is absorbed and temperature drops.
B.
- Cyclohexane has to be used in excess in order to ensure that no hydrogen bond is presented.
- The hydrogen bond strength obtained was not accurate because there is heat lost to surroundings and to the beaker, which was not considered in calculation.
C.
- The temperature rises. During mixing, the electropositive hydrogen atom in trichloromethane formed hydrogen bonds with the electronegative oxygen atom in ethyl ethanoate. As bonds are formed, energy is given out. Therefore the temperature rises.
D.
- It does not matter whether using trichloromethane or ethyl ethanoate in excess because using trichloromethane or ethyl ethanoate in excess does not affect the no. of hydrogen bonds per molecule.