Heat of Combustion

Ryan Tsinigine

Partner: Yuchen

Title: Heat of Combustion

CHM 151 LL

Wednesday: 11:15-2:00

Instructor: Dr. Leary

March 27, 2013

Introduction

In this lab we will be applying Hess’s Law to predict the enthalpies of an overall reaction. Hess’s Law simply states that the change in heat for an overall reaction is the sum of the change in heat values for the individual reactions. We will figure out the heat of combustion of Magnesium by carrying out a series of steps of reactions to determine the enthalpy change.

Procedure

1. Obtain a strip of magnesium approximately 2 cm long

2. Obtain 10 mL of 1.0 M HCl aqueous solution in 10 mL beaker

3. Obtain a Styrofoam cup and lid, temperature sensor and ring stand

4. Record mass of solid, magnesium ribbon

5. Measure 7 mL of HCl in graduated cylinder and pour into Styrofoam cup

6. Record initial temperature of HCl, room temp

7. Place magnesium ribbon into Styrofoam cup and record highest temperature reached

8. Shaking may be required to ensure full reaction

9. Repeat steps three times and record data for best results

Observations, Data, and Results

| Mg | MgO | Mg | MgO |

Initial Temperature, degrees Celsius | 22.7 | 23.0 | 22.7 | 23.3 |

Max Temperature | 39.9 | 29.9 | 45.0 | 30.5 |

Temperature Change | 17.2 | 6.90 | 22.3 | 7.20 |

Mass of solid, mg | 0.025g | 0.58g | 0.035g | 0.56g |

Empty beaker + Styrofoam cup + cardboard cover | 112.15g | 112.17g | 112.17g | 112.17g |

Beaker + Styrofoam Cup + cardboard cover + 7 mL HCl | 116.48 | 119.12g | 119.12g | 119.12g |

Mass of 7 mL | 4.33g | 6.95g | 6.95g | 6.95g |

Mass of solution | 4.36g | 6.99g | 7.53g | 7.51g |

Calculations

Mg(s) +.5O2(g) = MgO(s)

Conclusion

Based on our data we have determined the unknown alkali carbonate is potassium. Although our second trial was off in grams of m but we have concluded that it was due to technical or human error. Our percent experimental error is 98.4 percent which is...