To determine the enthalpy of reaction.

Calculation

• Polystyrene

• CaCo3(s)  + 2HCl(aq)→  CaCl2(aq) + Co2(ga) + H2O(l)

• Find the number of mole

n = m

      M

n = 2.52

                            100

n = 0.0252mol

     

• Heat evolved in the reaction

                     

                      ΔH1 = mcΔT1

                      ΔH1 = 2.52g x 4.2 J/gk x (22oc-20oc)

                      ΔH1 = 21.168J

ΔH1 = 21.168/1000 J

ΔH1 = 21.168 x 10-3 kJ

• Heat evolved per mol

       ΔH1

         n

      21.168 x 10-3 kJ

        0.0252 mol

    ΔH1 =  0.84 kJ/mol

• CaO(s) + 2HCl(aq) → CaCl2(aq) + H2O(l)

• Find the number of moles for CaO

n = m/M

n = 2.52/52

n = 0.0485mol

• Heat evolved during the reaction (ΔH2)

ΔH2 = mcΔT2

ΔH2 = 1.5 x 4.2 x (40.5oc-18oc)

ΔH2 = 141.75J

ΔH2 = 0.14175 kJ

• Heat evolved per mol

                      ΔH2/n = 0.14175 kJ /0.0485

                       ΔH2 = 2.92KJ/mol

• ΔH3 = ΔH1 - ΔH2

      ΔH3 = 0.84KJ/mol – 2.92KJ/mol

      ΔH3 = -2.08KJ/mol

• Glass beaker

• CaCo3(s)  + 2HCl→  CaCl2(aq) + Co2(ga) + H2O(l)

•       Find the number of moles for CaCo3

n = m/M

n = 2.52/100

n = 0.0252mol

                       

               

• Heat evolved in the reaction

                     ΔH1 = mcΔT1

                     ΔH1= 2.52 x 4.2 x (21oc-20oc)

                     ΔH1 = 10.584J

                     ΔH1 = 0.010584 kJ

• Heat evolved per mol

                       ΔH1/n = 0.010584KJ/0.0252mol

 

ΔH1 = 0.42 KJ/mol

• CaO(s) + 2HCl(aq) → CaCl2(aq) + H2O(l)

• Find the number of moles for CaO

n = m/M

n = 2.52/52

n = 0.0485mol

• Heat evolved during the reaction (ΔH2)

 

          ΔH2 = mcΔT2

          ΔH2 = 1.5 x 4.2 x (36.5oc-18oc)

          ΔH2 = 116.55J

          ΔH2 = 0.11655KJ

•  Heat evolved per mol

                     ΔH2/mole = 0.11655KJ/0.0485 mol

                     ΔH2 = 2.4KJ/mol

• ΔH3 = ΔH1 - ΔH2

ΔH3 = 0.42KJ/mole –2.4KJ/mole

ΔH3 = -1.98KJ/mol

Conclusion

From the above calculation it is clear to see ΔH3 in a glass beaker is more than ΔH3 in the polystyrene. In other word it means ΔH3 that is -1.98KJ/mol (glass beaker) amount of heat was realised while –2.08KJ/mol amount of heat was realised when I use polystyrene. The difference is due to the property of the polystyrene and glass beaker, polystyrene is a thermal insulator that helps to keep the heat lost to the environment, whereas glass beaker is a poor insulator of heat due to this it loss heat to the environment very fast. If the glass beaker can not keep heat it is obvious to loss certain amount of heat.

Evaluation

The results of this investigation are as I predicted in the hypothesis. The amount of heat realised using glass beaker is lower than heat realised using polystyrene. The negative sign indicate the reaction was exothermic. The more the negative value we get the less heat lost to the environment.

• I use one thermometer to avoid any source of error.

• I make sure the equipments were clean and dry.

• I used a different weighing bottle to measure CaCO3 and CaO.

• I was controlling my self when I was transferring those powders.  

However, there are a number of errors might happen during the experiment:

1. There is a transfer error; some amount of CaCO3, CaO remain in the weighing bottle while I was transferring to the glass beaker and polystyrene.
2. Reading of the thermometer (I can only read to accuracy of nearest degree).
3. Measuring of the weight of CaCO3 and CaO.
4. Some errors are likely to come from measurements. A source of error would be parallax error, which would involve the meniscus.

Suggestions and Improvements - To create a more accurate experiment in the future, several precautions or alterations can be made:

• Cover both polystyrene and glass beaker to avoid heat loss to the environment
• Stir the solution in the same manner to get the maximum heat lost.

• It will be a god idea to do the investigation more than one so that an average of heat loss could be calculated.

Bibliography:

Chemistry 1 Endorsed by OCR