   Chapter 5, Problem 56PS

Chapter
Section
Textbook Problem

(a) Write a balanced chemical equation for the formation of 1 mol of MgO(s) from the elements in their standard states. (Find the value for ΔfH° for MgO(s) in Appendix L.)(b) What is the standard enthalpy change for the reaction of 2.5 mol of Mg with oxygen?

(a)

Interpretation Introduction

Interpretation:

The balanced equation for the formation of one mole of MgO is to be identified.

Concept Introduction:

Balanced reaction is a chemical reaction in which number of atoms for each element in the reaction and the total charge are same on both reactant side and the product side.

Steps in balancing the information

• Step 1: Write the unbalanced equation
• Step 2: Find the coefficient to balance the equation.

The coefficient should be reduced to the smallest whole number

Explanation

The unbalanced equation for the reaction is Mg +O2MgO. The equation can be balanced by multiplying the atoms with appropriate number, in the above equation, on the left one magnesium atom and two oxygens and on the right hand side one magnesium atom and one oxygen atom.

The balanced equation is Mg+1/2O2<

(b)

Interpretation Introduction

Interpretation:

The enthalpy change for the formation of one mole of MgO has to be determined.

Concept Introduction:

If a reaction proceeds in two or more other reaction,ΔrH0 for the overall process is the sum of ΔrH0 values of those reactions-Hess’s law.

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