Chem 2 test 1 – Flashcards

Heat of fusion refers to the change between the solid and the liquid states and heat of vaporization refers to the change between liquid and gas states. In the change from solid to liquid, the kinetic energy of the molecules must increase only enough to partially offset the intermolecular attractions between molecules. In the change from liquid to gas, the kinetic energy of the molecules must increase enough to overcome the intermolecular forces. The energy to overcome the intermolecular forces for the molecules to move freely in the gaseous state is much greater than the amount of energy needed to allow the molecules to move more easily past each other but still stay very close together.

The net force holding molecules together in the solid state is greater than that in the liquid state. Thus, to change solid molecules to gaseous molecules in sublimation requires more energy than to change liquid molecules to gaseous molecules in vaporization

At a given temperature and pressure, the magnitude of change in heat of vap is the same as the magnitude of change in heat of cond. The only difference is in the sign: change of heatvap = -change in heat cond.

In closed containers, two processes, evaporation and condensation, occur simultaneously. Initially there are few molecules in the vapor phase, so more liquid molecules evaporate than gas molecules condense. Thus, the number of molecules in the gas phase increases, causing the vapor pressure of hexane to increase. Eventually, the number of molecules in the gas phase reaches a maximum where the number of liquid molecules evaporating equals the number of gas molecules condensing. In other words, the evaporation rate equals the condensation rate. At this point, there is no further change in the vapor pressure.

a) At the critical temperature, the molecules are moving so fast that they can no longer be condensed. This temperature decreases with weaker intermolecular forces because the forces are not strong enough to overcome molecular motion. Alternatively, as intermolecular forces increase, the critical temperature increases. b) As intermolecular forces increase, the boiling point increases because it becomes more difficult and takes more energy to separate molecules from the liquid phase. c) As intermolecular forces increase, the vapor pressure decreases for the same reason given in b). At any given temperature, strong intermolecular forces prevent molecules from easily going into the vapor phase and thus vapor pressure is decreased. d) As intermolecular forces increase, the heat of vaporization increases because more energy is needed to separate molecules from the liquid phase

When water at 100°C touches skin, the heat released is from the lowering of the temperature of the water. The specific heat of water is approximately 75 J/mol•K. When steam at 100°C touches skin, the heat released is from the condensation of the gas with a heat of condensation of approximately 41 kJ/mol. Thus, the amount of heat released from gaseous water condensing will be greater than the heat from hot liquid water cooling and the burn from the steam will be worse than that from hot water.

Yes, every molecule has dispersion forces, and they are the weakest intermolecular force, so the dipole moment in polar molecules overpowers the dispersion force.

Polarity has a permanent imbalance in the distribution of electrons in the molecule. Polarizability is the ability of the electron distribution in a molecule to change temporarily. The polarity affects dipole-dipole interactions, while the polarizability affects dispersion forces.

If the electron distribution in one molecule is not symmetrical, it can induce a temporary dipole in an adjacent molecule by causing the electrons in that molecule to shift.

A) Hydrogen bonding B) Dispersion C) Dispersion

A) dipole-dipole B) Dispersion C) Hydrogen bonding

A) I- because the iodine ion is larger B) CH3=CH3 because they are part of pi bonds C) H2Se because Selenium is larger than Oxygen

A) C4H8 because it has less bonds to break to boil B) PBr3 because the dipole-dipole forces are weaker than the ionic forces in Sodium Bromide C) HBr the dipole-dipole forces are weaker than the hydrogen bonding forces of water

The ethylene glycol molecules have two sites (two -OH groups) which can hydrogen bond; the propanol has only one -OH group.

The strength of the forces does not change, but the KE of the molecules increases, and can overcome the intermolecular forces easier as they're heated. The molecules have more energy at higher temperatures, so they can break the intermolecular forces and can move more easily past their neighbors; thus, viscosity decreases.

Pentanol is more viscous because of the Hydrogen bond unlike hexane.

As n increases, that increases the hydrophobic CH molecules, making the compound less soluble in water.

a) Hydrogen bonding occurs between the H atom on water and the lone electron pair on the O atom in dimethyl ether (CH3OCH3). However, none of the hydrogen atoms on dimethyl ether participates in hydrogen bonding because the CH bond does not have sufficient polarity. b) The dipole in water induces a dipole on the Ne(g) atom, so dipole-induced dipole interactions are the strongest intermolecular forces in this solution. c) Nitrogen gas and butane are both nonpolar substances, so dispersion forces are the principal attractive forces

a) hydrogen bonding is the strongest type of intermolecular force in CH3OCH3 b) dipole induced dipole interactions are the strongest because the dipole in water induces a dipole in Ne c) dispersion forces are the strongest because they are both nonpolar

a) CH3CH2OCH3 is more soluble because it's smaller b) CH2Cl2 is more soluble because it's more polar

a) Entropy increases as the gasoline is burned. Gaseous products at a higher temperature form. b) Entropy decreases as the gold is separated from the ore. Pure gold has only the arrangement of gold atoms next to gold atoms, while the ore mixture has a greater number of possible arrangements among the components of the mixture c) Entropy increases as a solute dissolves in the solvent

a) entropy increases b) entropy decreases c) entropy increases

An increase in temperature produces an increase in kinetic energy; the gaseous solute molecules overcome the weak intermolecular forces, which results in a decrease in solubility of any gas in water. In nearly all cases, gases dissolve exothermically.

a) Increasing pressure for a gas increases the solubility of the gas according to Henry's law. b) Increasing the volume of a gas causes a decrease in its pressure (Boyle's law), which decreases the solubility of the gas.

Solubility of gases increases with increasing partial pressure of the gas, and the goal of these devices is to increase the amount of oxygen dissolving in the bloodstream

The boiling point temperature is higher and the freezing point temperature is lower for the solution compared to the solvent because the addition of a solute lowers the freezing point and raises the boiling point of a liquid.

The vapor pressure of H2O above the pure water is greater than that above the sugar solution. This means that water molecules will leave the pure water and enter the sugar solution in order to make their vapor pressures closer to equal.