Q & A Review Sessions

Announcements    Exam #1: Tuesday, September 25th, 7:00-8:15pm, locations on website Conflict Exam: 5:15-6:30pm, 114 Transportation Bldg, sign u...
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Announcements 





Exam #1: Tuesday, September 25th, 7:00-8:15pm, locations on website Conflict Exam: 5:15-6:30pm, 114 Transportation Bldg, sign up outside of 101 CA until noon on 9/25 Review Questions for Exam 1 due tomorrow by 5:00pm

Q & A Review Sessions TAs

Sections

Zack Gordon BDB, BDC, BDE, Doug Rybar BDJ, BDK, BDM Nitin Neelakantan Liz Ohr BDD, BDF Anna Wetherholt Alex Stanton BDA, BDG, BDI Puzhou Wang Lauren Cunningham BDH

Derek Le

BDL

Time and Location Sept. 23 (Sun) 1-3 pm 217 Noyes Lab Sept. 23 (Sun) 4-6 pm 161 Noyes Lab Sept. 20 ( Thurs) 7-9 pm 1002 Lincoln Hall Sept. 23 (Sun) 7-9 pm 165 Noyes Lab Sept. 20 (Thurs) 5-7 pm 162 Noyes Lab

Demo: motion of gas 



  

Can filled with balls – model of gas in container Pressure (P): can “hear” pressure (collisions with sides of can) Volume (V): size of can Moles (n): number of balls (amount of gas) Temperature (T): how fast you shake can

Demo: motion of gas 

How would you increase the pressure? 

 



Increase moles (more balls) Decrease volume (smaller can) Increase temperature (shake faster)

Gets us to idea of WHY we observe these relationships between P, V, n and T

Pressure: Microscopic Why do we observe pressure?  Collisions of gas particles with walls of container  To increase pressure:  increase number of collisions (faster particles)  increase force of the collisions (heavier particles)

Partial Pressures 

Pressure is additive P(total) = P1 + P2 +P3….



Example: container with N2 and H2



 



same volume for P(N2) and P(H2) same temperature for P(N2) and P(H2)

Important when doing problems involving partial pressure

Temperature and energy 



 

Temperature is measure of average kinetic energy of a sample Related to average velocity of gas particles and mass KE = ½ mv2 Energy of movement, how fast particles are moving

Temperature and motion DEMO: Hot versus cold  Drop food coloring into beaker of cold water and beaker of hot water  Which spreads faster?  Food coloring spreads faster in hot beaker because molecules are moving and colliding faster than molecules in cold beaker

Kinetic Molecular Theory Gases are made of particles in constant random motion.  Temperature is a measure of random kinetic energy.  Pressure is due to collisions of gas particles with container. 

KMT (assumptions) 



Assume that gas particles exert no attractive forces (elastic collisions). Assume volume of gas particles is negligible (zero).

KMT (Assumptions) 





Assumptions are more likely to be true if:  High temperature (very hot)  Large volume (to move around in)  Low pressure This will cause gas molecules to hit less often (which gets around “attractive” forces)

But let’s talk about mass and pressure now

Clicker #1



The two balloons above are the same size but contain different gases. How do the pressures inside the balloons compare? A) B) C) D)

The pressures are the same. The balloon with helium (He) has the greater pressure. The balloon with xenon (Xe) has the greater pressure. Not enough information is given to answer this question.

Clicker #2



The two balloons above are the same size but contain different gases. Which gas particles will hit the walls of the balloon harder? A) B) C)

They both hit with the same amount of force. The helium particles will hit harder. The xenon particles will hit harder.

Mass and pressure 



 

Why does Xe hit the wall harder?  because it has a larger mass Why does He have the same pressure then?  Because He moves faster and makes up for the mass difference Heavier gas particles move slower Lighter gas particles diffuse faster

Clicker #3 

You are holding three balloons each containing the same mass of gas. One balloon contains hydrogen gas, one contains helium, and one contains oxygen. Which balloon is the largest?

A) B) C) D)

The hydrogen balloon is the largest. The helium balloon is the largest. The oxygen balloon is the largest. All of the balloons are the same size.

Example 

You are holding three balloons each containing the same mass of gas. One balloon contains hydrogen gas, one contains helium, and one contains oxygen. Draw the relative sizes of these balloons. (Assume P and T are constant)



A 50.0-L steel tank contains 186 mol N2 and 145 mol O2 at 24oC. What is the partial pressure of each gas in the tank? What is the total pressure in the tank?

Consider a sample of gas at 2.00 atm in a 35.0-L container at 25.0oC. You transfer all of the gas to a 70.0-L container and you heat the gas to 50.0oC. Determine the new pressure of the gas.

Consider a sample of gas at 5.40 atm in a 1.00-L rigid container at 40.0oC. You heat the gas to 80.0oC. What happens?

Solve for the new condition.

Consider a sample of gas at 5.40 atm in a 1.00-L container fitted with a piston at 40.0oC. You heat the gas to 80.0oC. What happens?

Solve for the new condition.