Chemistry Chapter 10 Discovering Design with Chemistry Dr. Jay Wile

CC 7: A sample of gas that contains 12.5 moles is at a pressure of 735.6 torr. If it occupies a volume of 0.45 kiloliters, what is its temperature?

420 K

CC 9: A chemist is making hydrogen gas by reacting zinc and HCl: Zn (s) + 2HCl (aq) -> ZnCl2 (aq) + H2 (g) if He has an excess of zinc and 850.0 ml of 5.0 M HCl, what volume of H2 will be made at STP

49 L

Review 3: What does a barometer measure?

A barometer measures atmospheric pressure using mercury.

Review 2: What is a Pascal?

A pascal is a standard unit of force; N/m^2

Review 15: IN each case, indicate which of the two situations will be most likely to produce ideal behavior in a gas: a. (1) T= 124 K, P= 1 atm or (2) T = 280 K, P= 1 atm b. (1) T= 275 K, P= 700 torr or (2) T= 275 K, P= 4,567 torr c. (1) STP or (2) T= 100 K, P= 15 atm

A. Situation 2 B. Situation 1 C. Situation 1

CC 5: in each of the following cases, choose the situation that would result in the gas behaving most ideally. a. (1) one mole of gas at 275 K or (2) one mole of gas at 350 K. b. (1) one mole of gas at 740 torr or (2) one mole of gas at 1,500 c. (1) one mole of gas in a very small container or (2) one mole of gas in a much larger container d. (1) one mole of H2 gas or (2) one mole of C12H4Cl4O2 gas under the same conditions

A. Situation 2 B. Situation 1 C. Situation 2 D. Situation 1

Charles Law

At a constant pressure, temperature and volume are directly proportional to one another

Boyle's Law

At a constant temperature, pressure and volume are inversely proportional to one another.

CC 11: Suppose you are camping at Leavitt Lake in California, which is at an altitude of about 3,050 meters. The atmospheric pressure there is 522 torr. will water boil at a temperature above or below 100 degrees Celsius, between 90 and 100 degrees Celsius, between 60 and 90 degrees Celsius, or below 60 degrees Celsius?

Between 60 and 90 degrees Celsius

Avogadro's Law

Equal volumes of all gases at the same temperature and pressure have the same number of molecules (or atoms, if the gas is not made of molecules)

Extrapolation

Extending a trend in data to situations for which no measurements have been made

CC 4: A balloon is floating on the surface of lake. Its volume is 3.91 liters, its pressure is 1.09 atm, and its temperature is 28.4 degrees Celsius. It is then pulled to the bottom of the lake, where the pressure is 3.70 If its new volume is 1.09 liters, what is the temperature at the bottom of the lake in degrees Celsius?

In this case, nothing is held constant. The pressure, volume, and temperature when it is floating on the surface represent P1, V1, and T1, while the pressure, volume, and temperature at the bottom of the lake are P2, V2, and T2. Before we use the equation, however, we need to get the temperature into Kelvin. THen we can use Equation (10.5). To solve for T2, we need to multiply both sides of the equation by T2 and 301.6 K. Then, we need to divide both sides by 1.09 atm and 3.91 L. Then convert to Celsius

Review 7: What does it mean for a temperature scale to be an absolute temperature scale?

It means you can never get to or below zero on that scale

Review 4: Why are inches of mercury and millimeters of mercury used as units for pressure?

Mercury is used because they refer to the height of the column of mercury in a barometer, and that's how a barometer measures pressure

CC 10: In a mixture of two gases, the partial pressure of oxygen is 341 torr, while the partial pressure of nitrogen is 761 torr. If there are a total of 6.78 moles of gas, how many moles of oxygen and nitrogen are present?

Moles of component A

CC 6: A sample of gas contains 18.45 moles at STP. What volume does it occupy?

Since the gas is at STP, we know it has a pressure of exactly 1 atm and a temperature of exactly 0 degrees Celsius. As you saw in the example, that's the same as a temperature of 273.15 K. Since we are given the number of moles and are supposed to have R memorized, it is easy to solve for volume. This equation leaves you with the answer of 414 L.

CC 3: A gas is compressed under constant temperature. It starts out with a volume of 150.1 mL and ends up with a volume of 75.6 mL. If the initial pressure was 750 torr, what is the final pressure?

Since the temperature is constant, T1 and T2 are the same to they cancel. Now we can plug in what we know. 150.1 mL goes with 750 torr because 150.1 mL is the starting volume, and 750 torr is the initial pressure. that makes them V1 and P1. that means 75.6 mL is V2. Dividing both sides by 75.6 allows us to sovle for P2 giving us 1,500 torr.

Review 5: If you inflate a balloon into a container and then add lots more pressure to the container without changing the temperature, what will happen to the size of the balloon?

The balloon's size will decrease.

Review 6: If you inflate a balloon at room temperature scale to be an absolute temperature scale?

The balloon's size will decrease.

Review 22: A camper boils water to cook dinner. He cooks the same dinner two nights in a row but it takes longer for the same amount of the same dinner to cook on the second night. Compare the atmospheric pressure he experiences on the two nights.

The boiling point depends on the atmospheric pressure, because it is defined as the temperature at which the vapor pressure of the liquid equals the surrounding pressure. Since it took longer to cook the same meal on the second night, that means water was boiling at a lower temperature. that must mean the atmospheric pressure was lower the second night.

Review 8: What is the boiling point of water at 1 atm in Kelvin?

The boiling point of water at 1 atm is 373.15 K. At 1 atm, the boiling point of water is defined to be 100 degrees Celsius which is exact. to convert to Kelvin, we use Equation (10.4) -K= Degrees C + 273.15= 100 + 273.15= 373.15)

Review 23: A chemist makes hydrogen gas according to the equation: 2Mg (s) + 2HBr (aq) -> MgBr2 (aq) + H2 (g) She collects the hydrogen over the water in which the reaction is taking place. If she collects 3.41 liters of Hydrogen at 0.981 atm and 60.0 degrees Celsius, how many moles of hydrogen gas did she make?

The chemist made 0.0977 moles. We can't use the Ideal Gas Law immediately, because the gas is collected over water. Thus, it is a mixture of hydrogen and water vapor. To subtract out the water vapor, we need the vapor pressure of water at 60.0 degrees Celsius. The table on page 311 says it is 149.4 torr. However to use the Ideal Gas Law, That has to be in atm

Review 20: A balloon is filled with 345 torr of oxygen gas and 416 torr of nitrogen gas. What is the mole fraction of each gas?

The mole graction of oxygen is 0.453, and the mole fraction for nitrogen is 0.547. The mole fraction is related to the partial pressure and total pressure. we have the partial pressures, so we just have to get the total pressure:

Review 21: A container holds 0.34 moles of chlorine gas, 0.22 moles of xenon gas, and 0.56 moles of krypton gas. If the total pressure of the gases is 1.1 atm, what is the partial pressure of each gas?

The partial pressures are .33 atm for chlorine, .22 atm for xenon, and .55 atm for krypton. Equation (10.9) allows us to figure out the partial pressure of each gas if we know the mole fraction.

Review 14: A helium-filled balloon has a volume of 35.4 liters at an altitude where the temperature is 0.00 degrees Celsius and the pressure is 0.619 atm. It is brought back to the ground, where the temperature is 22.90 degrees Celsius and its volume is 21.1 liters. what is the pressure on the ground?

The pressure is 1.13 atm.

Boiling point

The temperature at which a liquids vapor pressure is equal to the external air pressure

Review 9: Nitrogen condenses at 77 K. What is the temperature in degrees Celsius?

The temperature is -196 degrees Celsius

Review 13: a flexible container is held at constant pressure. it starts with a volume of 1.2 liters at a temperature of 25 degrees Celsius. What is the volume if the temperature rises to 50.0 degrees Celsius?

The volume is 1.3 L.

Review 19: A chemist burns 567 liters of propane (C3H8) how many liters of carbon dioxide are made at 1.04 atm and 1,995 degrees Celsius? C3H8 (g) + 5O2 (g) -> 3CO2 (g) + 4H2O (g)

The volume is 170x10^3 L. We could use the Ideal Gas Law, but since the things we are interested in are both gases, we can just use Avogadro's Law and allow the chemical equation to give us the relationship between the volumes.

Review 17: what is the volume of 10.0 grams of water vapor at 134.5 degrees Celsius and a pressure of 567 torr?

The volume is 24.9. There is no relationship among grams, volume, pressure, and temperature for a gas, but the Ideal Gas Law relates moles, volume, pressure, and temperature, as long as pressure is in atm and temperature is in K. Thus, we must get from grams to moles and convert the pressure and temperature to the right units.

Review 12: a piston contains 45.6 mL of gas at a pressure of 814 torr. If the temperature doesn't change, what is the volume of the gas at a pressure of 760.0 torr

The volume is 48.8 mL.

Review 16: How many moles of nitrogen are present in a 891 mL container at 23.0 degrees Celsius and 345 torr?

There are 0.0166 moles of nitrogen. The Ideal Gas Law relates mole to pressure, volume, and temperature, but the units need to be atm, liters and K

Review 18: in the following decomposition of 150.0 grams of potassium chlorate (KCIO3), what volume of oxygen is made at STP? 2KCIO3 (s) -> 2KCI (s) + 3O2 (g)

There are 41.2 L of oxygen gas produced. If we want to get the volume of oxygen, we will need to figure out the moles of oxygen. We can get that by doing stoichiometry.

CC 2: A chemical reaction is run at a temperature of 156.7 K. What is the temperature in degrees Celsius and degrees Fahrenheit?

To get to the Celsius scale, we just use Equation (10.4). Remember, this is subtraction, so the significant figures are determined by precision. The 156.7 is the least precise number, so the answer must have the same precision. Now we can use Equation (6.1) to get the temperature in the degrees Fahrenheit.

Review 11: Why must you use an absolute temperature scale like the Kelvin scale when working with the gas laws?

Using the gas laws often involves dividing by temperature, and you cannot divide by zero. Thus, you must use a scale that doesn't have a zero in it.

Review 10: Fill in the blank: When extrapolating, a good scientist keeps the range of extrapolation ______ compared to the range over which the data have been measured.

When extrapolating, a good scientist keeps the range of extrapolation SMALL compared to the range over which the data have been measured.

CC 1: a barometer reads a pressure of 750.1 torr. How many atmospheres (atm) is that? Is it above or below the average atmospheric pressure found at sea level?

since the numbers in the conversion relationship are exact, the significant figures are determined y the original measurement. Since there are four significant figures in 750.1, there need to be four in the answer. this is below the average atmospheric pressure at sea level, since that's defined as 1 atm.

CC 8: A chemist is making ammonia gas according to the following equation: N2 (g) + 3H2 (g) -> 2NH3 (g) If she starts with 150.0 liters of N2 and an excess of H2 at STP, what volume of NH3 will be made at STP?

you could use the Ideal Gas law to convert the volume of N2 into moles, then get the moles of NH3 and then use the Ideal Gas Law to convert that back to volume. However, since the pressure and temperature are constant (STP the entire time), and since both substances are gases, we can just use Avogadro's Law, which tells us the chemical equation gives us the relationship between the volumes of the gases involved leaving us with 300.0 L NH3