V p x v x d 3 f x d w f d 2 v 0 p v 0 w sys 0 work is

This preview shows 10 out of 21 pages.

V P x V = x d 3 = F x d = w F d 2 V > 0 -P V < 0 w sys < 0 Work is not a state function. w = w final - w initial initial final
Image of page 10

Subscribe to view the full document.

11 A sample of nitrogen gas expands in volume from 1.6 L to 5.4 L at constant temperature. What is the work done in joules if the gas expands (a) against a vacuum and (b) against a constant pressure of 3.7 atm? w = - P V (a) V = 5.4 L – 1.6 L = 3.8 L P = 0 atm W = -0 atm x 3.8 L = 0 L•atm = 0 joules (b) V = 5.4 L – 1.6 L = 3.8 L P = 3.7 atm w = -3.7 atm x 3.8 L = -14.1 L•atm w = -14.1 L•atm x 101.3 J 1L•atm = -1430 J
Image of page 11
12 Heat, q, is also not a state function. You can heat water with a Bunsen burner without doing any work on the water. Also, you can heat the water by other means
Image of page 12

Subscribe to view the full document.

13 Chemistry in Action: Making Snow U = q + w q = 0 (no heat exchange, adiabatic process ) w < 0, U < 0 U = C T T < 0, SNOW!
Image of page 13
14 Enthalpy and the First Law of Thermodynamics U = q + w U = H - P V H = U + P V q = H and w = - P V At constant pressure:
Image of page 14

Subscribe to view the full document.

15 Enthalpy is a state function.
Image of page 15
16 Enthalpy (H) is used to quantify the heat flow into or out of a system in a process that occurs at constant pressure. H = H (products) – H (reactants) H = heat given off or absorbed during a reaction at constant pressure H products < H reactants H < 0 H products > H reactants H > 0
Image of page 16

Subscribe to view the full document.

17 Thermochemical Equations H 2 O ( s ) H 2 O ( l ) H = 6.01 kJ/mol Is H negative or positive? System absorbs heat Endothermic H > 0 6.01 kJ are absorbed for every 1 mole of ice that melts at 0 0 C and 1 atm.
Image of page 17
18 Thermochemical Equations CH 4 ( g ) + 2O 2 ( g) CO 2 ( g) + 2H 2 O ( l ) H = -890.4 kJ/mol Is H negative or positive? System gives off heat Exothermic H < 0 890.4 kJ are released for every 1 mole of methane that is combusted at 25 0 C and 1 atm.
Image of page 18

Subscribe to view the full document.

19 H 2 O ( s ) H 2 O ( l ) H = 6.01 kJ/mol The stoichiometric coefficients always refer to the number of moles of a substance Thermochemical Equations If you reverse a reaction, the sign of H changes H 2 O ( l ) H 2 O ( s ) H = - 6.01 kJ/mol If you multiply both sides of the equation by a factor n , then H must change by the same factor n . 2H 2 O ( s ) 2H 2 O ( l ) H = 2 x 6.01 = 12.0 kJ
Image of page 19
20 H 2 O ( s ) H 2 O ( l ) H = 6.01 kJ/mol The physical states of all reactants and products must be specified in thermochemical equations.
Image of page 20

Subscribe to view the full document.

Image of page 21
You've reached the end of this preview.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern