In this experiment, you will use this principle of Hess\' Law as you determine a

Question

In this experiment, you will use this principle of Hess' Law as you determine a heat of reaction that would be difficult to obtain by direct measurement-the heat of combustion of magnesium ribbon. The reaction is represented by the equation Mg(s) + 1/2 O_2 (g) rightarrow MgO (s) This equation can be obtained by combining equations (1), 2 and (3): MgO (s) + 2 HCl (aq) rightarrow MgCl_2 (aq) + H_2 O(l) Mg (s) + 2 HCl (aq) rightarrow MgCl_2 (aq) + H_2 (g) H_2 (g) + 1/2 O_2 (g) rightarrow H_2 O (l) Determine (calculate) the delta H values for reactions (1), (2) and (3). Use these values to determine the delta H value for equation (4). your work. In this experiment, you will Combine three chemical equations to obtain a fourth. Use prior knowledge about the additivity of reaction heats. Determine the heat of combustion of magnesium ribbon.

Explanation / Answer

1) MgO + 2 HCl MgCl2 +H2O Let heat of reaction be H1.

2)   Mg + 2 HCl MgCl2 +H2 Let heat of reaction be H2.

3) H2 + 1/2 O2 H2O Let heat of reaction be H3

Required equation is

4) Mg + 1/2 O2 MgO Let heat of reaction be H4.

Add equation (1) and (3) then substract (2), So we get

Mg + 2 HCl + H2 + 1/2 O2 - ( MgO + 2 HCl ) MgCl2 +H2 + H2O -(MgCl2 +H2O)

Cancelling terms on both sides we get

Mg + 1/2 O2 MgO

H4.=  H2 + H3 -  H1

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