5.enthalpy key

5.enthalpy key - Chem 105 Nielson Recitation Energy Work...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
Chem 105 Nielson Recitation 9/20/07 Energy Work Heat 1 st Law of thermodynamics State functions Enthalpy 1. H 2 and O 2 gases are combusted to make steam in a cylinder with a movable piston. As the reaction occurs, the system loses 1150 J of heat to the surroundings. The reaction also causes the piston to rise. The expanding gas does 480 J of work on the surroundings as it pushes up the piston. What is the change in the internal energy of the system? Ans. Since q = -1150 J and w = -480 J (notice the signs for q and w), then E = q + w = -1150 J + (-480 J) = -1630 J 2. What is meant by the term state function? Which of the following are state functions: Pressure, travel time, work, location, altitude, heat, temperature, enthalpy? For the properties that are not state functions, briefly explain why. Ans. A state function is the property of a system that is determined only by the physical state of the system, not on the route used to get to the current state. State functions do not depend on the pathway, only on the initial and final states. State functions include pressure, location, altitude, temperature, enthalpy. Travel time, work and heat are not state functions. Travel time is not a state function because the amount of time it takes to travel somewhere is always dependant on the path. Imagine driving to SLC on the freeway versus the side access road. The freeway is a much fast trip. Work is not a state function because the amount of work done on or by a system depends
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 12/09/2009 for the course CHEM 105 taught by Professor Macedone during the Spring '07 term at BYU.

Page1 / 3

5.enthalpy key - Chem 105 Nielson Recitation Energy Work...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online