Chemistry Unit 2 Test

Explain why the alcohol level in a thermometer falls when it is placed in a cooler fluid. (3 step process)

1. Transfer of energy from water to alcohol 2. Alcohol slows down 3. Volume contracts

Explain why the alcohol level in a thermometer rises when it is placed in a warmer fluid. (3 step process)

1. Transfer of energy from water to alcohol 2. Alcohol speeds up 3. Volume expands

Suppose that you lowered the temperature of a gas from 100 degrees celsius to 50 degrees celsius. By what factor do you change the volume of the gas?

First convert to kelvins. 100 c = 373 K 50 c = 323 K 373/323=1.1548 The factor is about 1.15

Use factors to calculate the new P, V, or T. Make a decision as to how the change affects the variable you are looking for.

If you want the number to go up, put the bigger number on top If you want the number to go down, put the smaller number on bottom

Suppose that 25.0 mL of a gas at 725 mm Hg and 20 degrees celsius is converted to standard pressure and temperature. What would the new volume be?

Initial: P - 725 mm Hg V - 25.0 mL T - 293 K (20 c) Final: P - 760 mmHg V - ? T - 273 K 25x725/760 = 23.849 23.849x273/293 = 22.22 The final volume is 22 mL (pay attention to sig figs)

Explain how the celsius scale was devised and why it is not appropriate to use it when describing the behavior of gases.

It was discovered that liquids froze at 0 degrees celsius and boiled at 100 degrees celsius. Celsius cannot be used when describing gases because the absolute zero of a gas is much lower than that of a liquid, so it has to be converted into Kelvins

Predict the effect of changing P, V, or T or any of the other variables.

P and V - inverse relationship (pressure goes up and volume goes down) P and T - direct relationship (pressure goes up and temperature goes up) V and T - direct relationship (volume goes up and temperature goes up)

Explain (in terms of the collisions of particles) why the change has the effect you predicted.

P and V - particles stay the same as pressure increases when volume decreases because there is less space for the particles to move, so they bounce off of each other more times creating more pressure P and T - Pressure increases when temperature increases because particles move faster at a higher temperature, making them bounce off of the sides of its container more times V and T - Volume increases when temperature increases because particles of a container, like a balloon, expand when they are heated up

Explain why one must use the Kelvin temperature scale to solve gas problems.

The absolute zero of a gas is much lower than that of a liquid, making it inaccurate to use when determining gas. We have to convert to Kelvins to make the absolute zero of the gas get closer to zero. (The temp is actually 273 Kelvin less than it should be when using celsius)

Find your copy of The Model so Far and note wha modifications in the particle model of matter we have made this unit.

We added whooshies