| Heat of Combustion |
Figure 1
Introduction According to Hess’s Law, if a reaction can be carried out in a series of steps, the sum of the enthalpies (total energy) of the individual steps should equal the enthalpy change for the overall reaction. In this experiment we will use Hess’s Law to analyze a reaction that would be difficult to understand just by direct measurement. We will study the heat of combustion of magnesium ribbon: Mg (s) + ½ O2(g) MgO(s) (1) This equation can be obtained by combining: MgO(s) + 2HCl (aq) MgCl2(aq) + H2O (2) MgCl2(aq) + H2(g) (3) Mg(s) + 2HCl(aq) H2 + ½ O H2O(l) (4) (g) 2(g) The heat of the reaction can be calculated using the following equation: đ?‘„ = đ?‘šđ??śâˆ†đ?‘‡ (5) Where: Q = The quantity of heat released or absorbed. m = The mass of the substance. C = The heat capacity of the substance. ď „T =The change in temperature.
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