Chemistry

Chapter 10 Study Questions

 

1.  For a reaction where DH = - 20 kJ,

      a)  Draw an energy diagram.

      b)  Is this reaction endothermic or exothermic?

      c)  In this reaction, which has greater heat content (enthalpy), reactants or products?

      d)  Is heat released or used up?

 

2.  Classify each of the following processes as endothermic or exothermic.

      a)  combustion of natural gas

      b)  condensation of water vapor

      c)  splitting of carbon dioxide into carbon and oxygen

      d)  solidification of melted wax

      e)  formation of sodium chloride (NaCl) from it elements

      f)  evaporation of alcohol

 

3.  Napthalene, C10H8, is often the active ingredient in mothballs.  H for the complete combustion of 1.00 mole of napthalene is -5159 kJ.

      a)  Write a balanced thermochemical equation for the complete combustion of napthalene.

      b)  Is this reaction endothermic or exothermic?

      c)  How many moles of carbon dioxide are produced when 258 kJ are given off?

      d)  How much heat is produced during the combustion of 1.86 g of napthalene?

 

4.  Use Hess' Law and the following equations: 

   Pb(s)  +  ½ O2(g)   ®   PbO(s)                     H  =  -217.9 kJ

3 Pb(s)  +  2 O2(g)    ®   Pb3O4(s)                   H  =  -734.7 kJ

to calculate DH for the following reaction, and indicate whether it is endothermic or exothermic:  6 PbO(s)  +  O2(g)   ®   2  Pb3O4(s).

 

5.  A 48.0 gram sample of lead absorbs 392 joules when it is heated from 25.0°C to 90.0°C.  What is the specific heat of lead?

 

6.  A styrofoam cup “calorimeter” is used to calculate the heat change when 5.03 g of NH4Cl are dissolved in 60.0 g water.  The initial temperature of the water in the cup is 24.78°C.  After the NH4Cl is added, the temperature in the cup is 19.23°C.

      a)  What is the temperature change of the water?

      b)  Is this process endothermic or exothermic?

c)  Calculate the heat change in Joules when the NH4Cl is dissolved in the water.  (Assume that the heat change for the solution is the same as that of water alone and that you can ignore the mass of solid in the water.  So use only the mass of water and the specific heat of water, 4.18 J/g °C, in calculating the heat change.)

d)  Calculate the number of moles of NH4Cl dissolved.

e)  Calculate the heat change per mole of NH4Cl in kJ/mol.


Summary of Chapter 10:  Energy

 

Potential and Kinetic Energy

Law of conservation of energy

1st and 2nd Laws of Thermodynamics

State functions

Temperature

endothermic, exothermic

heat content diagrams

specific heat

calorimetry:  calculation of heat change from temperature change

            Q  =  s  ×  m  ×  DT

Heat content = enthalpy

change in heat content (DH)

thermochemical equations

DH/mole conversions

Hess’ Law

Fossil fuels

            Petroleum, Natural Gas, Coal

Greenhouse effect

Entropy