Choose the substance with the highest viscosity: A) water at 10°C B) water at 20°C C) water at 30°C D) water at 40°C E) water at 50°C 13. What is the strongest type of intermolecular force present between NaCl and CHF2? A) dispersion B) dipole-dipole C) hydrogen bonding D) ion-dipole E) none of the above 14. Which of the following statements is TRUE? A) At a given temperature, lighter gas particles travel more slowly than heavier gas particles. B) The smaller the gas particle, the slower it will effuse. C) The higher the temperature, the lower the average kinetic energy of the sample. D) At low temperatures, intermolecular forces become important and the pressure of a gas will be lower than predicted by the ideal gas law. E) None of the above statements are true. 15. Some things take longer to cook at high altitudes than at low altitudes because: A) water boils at a lower temperature at high altitude than at low altitude. B) water boils at a higher temperature at high altitude than at low altitude. C) heat isn’t conducted as well in low density air. D) natural gas flames don’t burn as hot at high altitudes. E) there is higher moisture content in the air at high altitude. Part II: Short Answers and Calculations. 16. Vessel A contains CO2 at 0°C and 1 atm. Vessel B contains SO2 at 20°C and 0.5 atm. The two vessels are the same size. Which vessel contains more molecules? Which contains more mass? In which vessel is the average kinetic energy of molecules higher?
The Correct Answer and Explanation is:
Highest Viscosity of Water at Different Temperatures:
The viscosity of water decreases as the temperature increases. At lower temperatures, the molecules move more slowly and interact more strongly, resulting in higher viscosity. Conversely, as the temperature increases, the water molecules gain energy, move faster, and the viscosity decreases.
Therefore, water at 10°C has the highest viscosity, as lower temperatures lead to more molecular interactions that resist flow.
14. Strongest Type of Intermolecular Force between NaCl and CHF2:
NaCl is an ionic compound, and CHF2 is a polar molecule. The strongest intermolecular force between NaCl and CHF2 is the ion-dipole interaction. The negative or positive charge of the NaCl ions interacts with the partial charge on the CHF2 molecule, forming this force.
So, the correct answer is: D) ion-dipole.
15. True Statement Regarding Gas Particles:
Let’s break down the options:
- A) Lighter gas particles travel more slowly than heavier ones: This is false. According to the kinetic molecular theory, lighter particles have higher speeds at a given temperature because kinetic energy depends on mass and velocity.
- B) Smaller gas particles effuse slower: This is also false. Lighter, smaller particles effuse faster according to Graham’s law of effusion.
- C) The higher the temperature, the lower the average kinetic energy of the sample: This is false. Kinetic energy is directly proportional to temperature, so at higher temperatures, the average kinetic energy increases.
- D) At low temperatures, intermolecular forces become important, and the pressure of a gas will be lower than predicted by the ideal gas law: This statement is true. At low temperatures, gas molecules move more slowly, and intermolecular forces (which are neglected by the ideal gas law) become significant, causing the gas to deviate from ideal behavior. The pressure would be lower than predicted by the ideal gas law.
Thus, the correct statement is: D).
16. High Altitudes and Cooking Times:
At higher altitudes, the atmospheric pressure is lower, which lowers the boiling point of water. This means that water will boil at a lower temperature at high altitudes compared to sea level. Because the temperature at which water boils is lower, it takes longer to cook food, as the boiling water cannot reach as high a temperature as at lower altitudes.
Therefore, the correct answer is: A) water boils at a lower temperature at high altitude than at low altitude.
17. CO2 in Vessel A vs. SO2 in Vessel B:
To compare the two vessels, we need to apply the ideal gas law, PV=nRTPV = nRTPV=nRT, where nnn represents the number of moles of gas.
- More Molecules:
Given that the temperature in Vessel A (CO2) is lower and the pressure is higher, we would expect the gas in Vessel A to have more molecules since n=PVRTn = \frac{PV}{RT}n=RTPV. For the same volume, higher pressure and lower temperature would result in more molecules in Vessel A. - More Mass:
Mass is determined by the molar mass of the gas. CO2 has a molar mass of 44 g/mol, while SO2 has a molar mass of 64 g/mol. Even though the number of molecules in Vessel A (CO2) is greater, the mass in Vessel B (SO2) will be higher because SO2 has a higher molar mass. - Average Kinetic Energy:
The average kinetic energy of molecules is directly related to temperature and is given by KE=32kBTKE = \frac{3}{2} k_B TKE=23kBT, where kBk_BkB is the Boltzmann constant and TTT is temperature. Since Vessel B (SO2) is at a higher temperature (20°C vs. 0°C), the average kinetic energy of the molecules in Vessel B is higher.
In conclusion:
- Vessel A contains more molecules (due to higher pressure and lower temperature).
- Vessel B contains more mass (due to higher molar mass of SO2).
- Vessel B has a higher average kinetic energy (due to higher temperature).
