Welcome to Adobe GoLive 6

Annoucements

Chapter 6

Test for Chapter 6 is Thursday before break. If you arewill not be present on Thursday, you may take it on Wednesday the 22nd or the day you return from break.

WebAssign review for the midterm is now up. Begin early. It is long, but it is good exam practice and it is an important part of your second marking period grade.

Please look at chapter four on the Chang Online Learning Center. Go through the Essential Study Partner partial pressures at some point before returning from Thanksgiving.

Upcoming Asssignments

Monday 12/13 (pg. 235 6.17, 6.18, 6.20) answers

Due Tuesday (pg. 235, #6.21; pg. 236 #6.43) answers

Due Wednesday (pg. 237-239 #6.47, 6.72, 6.87 ) answers

Due Thursday (6.37, 6.38, 6.39, 6.40) answers

Retroproblem: If 27.6 mL of a 0.40 M barium hydroxide solution was required to titrate 20.0 mL of a hydrochloric acid solution to its endpoint.

What type of reaction is this?
Write a balanced equation including state symbols.
Write a net ionic equation for the reaction.
What is the concentration of the acid?

Remember:

Heat is a transfer of thermal energy between two bodies of different temperatures.

Temperature is a measure of an object's hottness.

Specific heat--the amount of energy required to raise 1 g of a substance by one degree C (or K)

To calculate the heat transferred to or from an object, use

Click to Hide

c_p= specific heat in J/g K. This is the amount of heat required to raise 1 g of a substance by one K. Lower specific heats mean a substance require less energy to get hotter, while high specific heats mean a more energy is required to change the temperature of the substance.

Low c_p are better conductors. These substance transfer (absorb and release) heat readily. Good conductors of heat are typically metals

High c_p are poor conductors. These substances resist changes in temperature. They do not transfer heat readily. (water, nonmetals)

If you are doing an experiment in a calorimeter some heat is transferred to the calorimeter.

If you are calculating the heat transfer from a hotter to a colder object (Temperature of a Bunsen flame experiment).

Note the above equation C is the heat capacity of the calorimeter units (J/^oC), so mass of the calorimeter is not needed.

If you are calculating the heat given off in a reaction,

Note the calculation is almost the same as the previous experiment. We usually, would like to report the value as a enthalpy change (delta H) in kJ/mol. To do this we have to divide q by a coefficient of the balanced chemical equation.

EXAMPLE PROBLEM: For example, a student reacted 0.45 g of Al metal with 50 mL of 1.0 M of an aqueous zinc chloride solution in a foam calorimeter to form aluminum chloride and zinc metal. The solution in the calorimeter went from 21.0 ^oC to 42.5 ^oC. Calculate the heat of reaction. Assume no heat was transferred to the calorimeter. Assume the specific heat of the solution is the same as water. Click here for the answer.

Hess's Law

Hess's Law states that the change in enthalpy for a process is not dependent on the reaction pathway. This allows you to calculate change in enthalpy theoretically. This is particularly useful when given standard enthalpies of formation. The last two assignments on the right are good practice using Hess's Law. You can calculate the change in enthalpy for a process two ways using Hess's Law. The first way is to algebraically manipulate chemical equations so they will sum to the net equation you are looking for. This techniques is utilized in problems 6.47, and 6.72 in your text (answer link to right). The other way is to use standard enthalpies of formations in the table at the back of your book (Appendix 3). This technique is used to perform 6.37 to 6.40 (solution link to right of page).