by horse Comment Closed

LARN 140 C35D4

Start the following in class:

1.  Write your journal entry on sheets of three holed 8.5 inch by 11 inch ruled paper in your Journal notebook. In the upper right corner white space of each upward facing page, write your hand in number within a circle followed by your name. Each journal entry should either be at least a paragraph of exemplary writing and penmanship concerning a single topic, or be a concept map relating chemistry terms. Begin each day’s paragraph with a topic sentence, follow with explained instances, and close with a focused summary statement.

1.a. The first required focus topic, J140A, for today is

a. Look up and record the magnitude and unit for the molar enthalpy of fusion for ice and the molar enthalpy of vaporization for water.

b. Place an =, >,  or < sign between the labeled values for the molar enthalpy of fusion for ice and the molar enthalpy of vaporization for water.

c. Use the particle theory of matter and the structural formula of water, knowledge of the type of bonding holding water molecules together in ice and in water, knowledge of what happens to the molecules of water when ice melts and knowledge of what happens to the molecules of water when water boils, to explain why the change in enthalpy for vaporization phase change is more than six times greater than the change in enthalpy for the other melting phase change.

1.b. Recall that:

  • Enthalpy is the term used in chemistry to designate the total energy (a.k.a. chemical potential energy content) of a chemical system when the total pressure of any gases present in the system is not changing (a.k.a. the system is at constant pressure).
  • A thermochemical equation is a chemical equation with a statement of the measured enthalpy change for the reaction as recorded in the balanced chemical expression being added to the right side of the chemical equation (after leaving a slight space to the right of the last products formula).
  • The change in enthalpy for reactions, ΔHrx, that are too slow to observe or which do not readily occur as written in a balanced equation can be determined by using Hess’ law.  Hess’ law states that the enthalpy change for a multistep process is equal to the sum of all of the enthalpy changes for each individual step of the process.  Hess’ law thus states that the thermochemical equation for a target chemical equation is equal to the sum of any set of thermochemical equations that produce the thermochemical equation for the target process when added together.
  • The standard state of a substance is a statement of the phase and formula for the phase the substance exists at 25.00 C [298.15 K] and 100.000 kPa pressure. (Standard pressure used to be defined as 101.325 kPa, which is almost the same value and which could also be considered correct.)
  • The standard enthalpy of formation, ΔHf°, for a substance is the amount of energy gained or liberated from the system when one mole of product substance is produced from the requisite moles of elements in their standard states.
  • The standard enthalpy of decomposition of a substance, ΔHd°, is the amount of energy gained or liberated from the system when one mole of reactant substance is decomposed into its elements in their standard states.

1.b. The second required focus topic, J140B, for today is:

What is the relationship between the standard enthalpy of formation, ΔHf°, for a substance and the standard enthalpy of decomposition for the same substance, ΔHd°?

2.  Study the discussion of the conversion of graphite to diamond using Figure 17.13 and Hess’ law on page 528 and the discussion of the burning of graphite to carbon monoxide gas using Figure 17.14 and Hess’ law on page 529.

  1. Then write full sentence responses to problems E17-57, E17-60, and E17-61 found on page 535.
  2. Then and only then do problems E17-59 and E17-74 on pages 535 and 536 using Hess’ law, ΔHnet rx = ΔHrx 1+ ΔHrx 2 + … + ΔHrx n =  ΔHrx 1→n for thermochemical equations that add up to the desired target thermochemical equation.
  • Be sure to line up arrows of the thermochemical equations to be added and compared.
  • Show the formula and phase of each reactant and product and the enthalpy change for each thermochemical equation on a single line and be sure to carefully line up quantities of reactants and products to be added to the left and right the arrows already written down.
  • Show the final value for the enthalpy change sought by circling it and expressing it to the proper number of significant figures.

     c. Study the discussion of the calculation of a standard enthalpy of reaction [a.k.a. standard heat of reaction] using Sample Problem 17.7 on page 531.

d. Then and only then do problems E17-69abc and E17-82 on pages 536 and 537 using

  • the table of standard heats of formation, Table 17.4 on page 530,
  • any standard heat of formation given in the problem, and
  • the relationship that ΔH =  ΔHf(products)– ΔHf(reactants).
  • Be sure to line up arrows of the thermochemical equations to be added and compared.
  • Show the formula and phase of each reactant and product and the enthalpy change for each thermochemical equation on a single line and be sure to carefully line up quantities of reactants and products to be added to the left and right the arrows already written down.
  • Show the final value for the enthalpy change sought by circling it and expressing it to the proper number of significant figures.

After you have finished responding to the formative assessment questions and problems, check page R97 of the text and check each of those problems that you can by writing in either a check mark (√) or a correction in green ink.  Write down any question that you still have so that you can ask about it in class.  In the margin of your notebook page, circle the number of formative assessment questions do not have a suggested response given and check your response with that of your classmates when you come to class.

Recommended for those who have time left in their 45 minute study period, but not required of all:

1.  Read and study the Study Guide given on page 534 of your text.  Review the Key Concepts for each text section and clarify in your mind under what circumstances would it be helpful to use each of the different relationships shown in the Key Equations section.

2. Continue to review the meanings of the words on the chapter 1, chapter 2, chapter 3, chapter 4, chapter 5, chapter 7, chapter 8, chapter 9, chapter 10, chapter 11, chapter 12, chapter 13, chapter 14, chapter 15, chapter 16, and chapter 17 vocabulary lists.  Place a – symbol in front of each word that you have to study more, and a change the- to a + symbol in front when you have demonstrated mastery over the word to a study buddy, parent, or friend.