FIRST- Find your NEW seats Bellringer: Grab a chemistry textbook and read pages , take 10 bullet notes HW Due: Any old homework or labs not turned in before spring break

Agenda Day 8 (extension of gas law unit) - Bellringer - Gas Law Unit Tests back - Notes & Demos on Dalton’s Law & section 13.2 in textbook - Prepare for lab next class HW for next class: 1. Read pages , take 10 bullet notes and complete problems 8, 11, 12, 13, & 14 AND 2. With your new lab partner write (or type) up a 1-page proposal for your “ten-minute lab” to be performed next week on energy

What questions do you have from the Gas Law Unit Test?

Going back to Dalton’s Law of Partial Pressures Remember: o P tot = P 1 + P 2 + P 3 + … P n o Where n is the total number of gases in the mixture. So what about your objective that states: “How Dalton’s Law of Partial Pressures applies to gases collected over water”? What does that mean and how is it useful? htm htm

Collecting gases over water While helpful there is the unavoidable problem. The gas saturates with water vapor and now the total pressure inside the bottle is the sum of two pressures - the gas itself and the added water vapor. WE DO NOT WANT THE WATER VAPOR PRESSURE. So we get rid of it by subtraction. P dry gas = P total - P water vapor

Pressure of Water Vapor This means we must get the water vapor pressure from somewhere. We get it from a table because the water vapor pressure depends only on the temperature, NOT how big the container is or the pressure of the other gas. Temp ( o C) Vapor Pressure (mmHg) Temp ( o C) Vapor Pressure (mmHg)

Dalton’s Law of Partial Pressures as it relates to collecting a gas over water directly relates to the lab we are going to complete next class

Practice Problem (Remember these problems often times involve the ideal gas law equation as well) A.) If 5.00 X moles of Hydrogen gas is formed by bubbling it up through water, it occupies a volume of mL at 22.0 o C. Using the moles of hydrogen determine the pressure of the dry Hydrogen gas B.) What is the total pressure including the water vapor?

Section 13.2 in text “A Model for Liquids” This section discusses o Evaporation o Vapor Pressure o Boiling Point What do any of those terms mean to you?

Evaporation Liquids may change to a vapor at temperatures below their boiling points through the process of evaporation. Evaporation is a surface phenomenon in which molecules located near the liquid's edge, escape into the surroundings as vapor (a gas). On the other hand, boiling is a process in which molecules anywhere in the liquid escape, resulting in the formation of vapor bubbles within the liquid. During evaporation, only those molecules with a certain minimum K.E. can escape from the surface of the liquid and become a gas. How would you predict that process of evaporation to change when you heat a liquid?

Vapor Pressure Definition: is the amount of gas/vapor pressure above a liquid in a closed system. Over time, the number of particles entering the vapor phase (liquid to gas) increases and some of the particles condense (gas to liquid) and return to the liquid state. Eventually, the number of particles condensing will equal (=) the number of particles vaporizing. Predict: How will vapor pressure change if you increase the temperature of a closed system (i.e. you increase K.E.)?

Trying to put it all together Boiling points at various altitudes Boiling water at room temperature ded&v=QGSo7zcg_qA# ded&v=QGSo7zcg_qA#!

So then, what’s Boiling Point? When a liquid is heated to a temperature at which particles throughout the liquid have enough kinetic energy to vaporize, the liquid begins to boil…but how will we know what temperature that is? A liquid boils when its vapor pressure is equal (=) to the external pressure The normal boiling point is defined as the boiling point of a liquid at atmospheric (standard) pressure: 1 atm or kPa or 760 torr or 760 mmHg or 14.7 psi

End of: Application of Dalton’s Law of Partial Pressures & Section 13.2 in Textbook HW for next class: 1. Read pgs , take 10 bullet notes and complete problems 8, 11, 12, 13, & 14 AND 2. With your new lab partner write (or type) up a 1-page proposal for your “ten-minute lab” to be performed next week on energy