C1210 lecture 15

C1210 lecture 15 - Suppose we know the easy-to-conduct...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
Suppose we know the easy-to-conduct reaction: C( s ) + O 2 ( g ) CO 2 ( g ) Δ H 0 = -393.5 kJ Because of conservation of energy we also know : CO 2 ( g ) C( s ) + O 2 ( g ) Δ H 0 = +393.5 kJ Even though we can’t run this (very energy uphill) reaction!!!!
Background image of page 1

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

View Full DocumentRight Arrow Icon
Let C and O 2 react: We’ll measure C( s ) + O 2 ( g ) CO 2 ( g ) Δ H 0 = -393.5 kJ Now conduct two, separate reactions and measure the Δ H 0 ’s: C( s ) + ½O 2 ( g ) CO( g ) Δ H 0 = -110.5 kJ CO( g ) + ½O 2 ( g ) CO 2 ( g ) Δ H 0 = -283.0 kJ Add ‘em up: C( s ) + ½O 2 ( g ) + CO( g ) + ½O 2 ( g ) CO( g ) + CO 2 ( g ) Δ H 0 = -110.5 - 283.0 kJ C(s) + O 2 (g) CO 2 ( g ) Δ H 0 = -393.5 kJ H is a state function, independent of path. • We can combine thermochemical equations to predict thermochemistry of reactions we haven’t observed!!!!!!!!!!!! A very big deal.
Background image of page 2
Δ H 0 = -393.5 kJ C( s ) + O 2 CO( g ) + ½O 2 CO 2 ( g ) Δ H 0 = -110.5 kJ Δ H 0 = -283.0 kJ An enthalpy diagram for the decomposition of CO 2 by two paths: C( s ) + O 2 ( g ) CO 2 and C( s ) + O 2 ( g ) CO + ½O 2 ( g ) Enthalpy is a state function: how we got from top to bottom is irrelevant. Remember, these enthalpies are differences relative to one another; we are dealing only with enthalpy differences . The levels are correct with respect to one another. We don’t know
Background image of page 3

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

View Full DocumentRight Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 12/10/2009 for the course CHE 1220 taught by Professor Jespersen during the Spring '09 term at St. John's.

Page1 / 9

C1210 lecture 15 - Suppose we know the easy-to-conduct...

This preview shows document pages 1 - 4. Sign up to view the full document.

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