MCAT Chemistry

phase diagram of carbon dioxide

- The transition of CO2 from its liquid phase to its solid phase will occur at lower temperatures, and pressures greater than 1 atm - CO2 will readily sublime into gas at 1 atm.

what is unique about the phase diagram of CO2

- liquid CO2 does not exist at atmospheric pressure - Therefore, in contrast to most other substances, which have a solid/liquid boundary that begins at pressures below 1 atm, the solid/liquid boundary for CO2 begins at pressures greater than 1 atm. - the CO2 phase diagram shows that fusion can only occur at pressures that are higher than 100 kPa.

1 atm is equivalent to

101 kPa 1.01 x 10^5 Pa

CO2 will readily sublime at what pressure

760 mmHg 1 atm 101 kPa

the molecular formula

A chemical formula that shows the number and kinds of atoms in a molecule, but not the arrangement of the atoms.

viscosity

A liquid's resistance to flowing ex: molasses has much higher viscosity than water

which equation is used to determine the change in temperature in response to added heat?

Q = mc(deltaT) where Q = heat (kJ) m = mass in kg c = specific heat capacity of a given substance in a specific state (solid, liquid, or gas)

pascal

SI unit of pressue equal to N/m^2

In a demonstration of liquid properties, a scientist pours out two different liquids from two separate beakers at the same time. Beaker A is filled with whole milk and beaker B is filled with olive oil. What is a valid explanation as to why one of the beakers will be emptied first?

Viscosity is the property of liquids by which they are resistant to flow, or the resistance to deformation by shear stress. On the molecular level, viscosity is caused by friction between layers of the fluid that are in motion relative to each other. Thus, fluids that have higher viscosity are more resistant to flow than those with lower viscosity. Since olive oil is more viscous than whole milk, beaker A will be emptied first.

empirical formula

a chemical formula that shows the composition of a compound in terms of the relative numbers and kinds of atoms in the simplest ratio

% yield

actual yield/theoretical yield x 100

Capillary action is due to the ______________.

adhesion of liquid molecules to the sides of the tube, which then pull lower liquid molecules upward by cohesion. Cohesive forces between liquid molecules

the pressure of the gas is determined by

amount of force that the gas molecules exert per area on the walls of a container, NOT the force exerted upon the gas molecules bouncing off each other.

capillary action is caused by

cohesion and adhesion

molecular solids are type of

crystalline solids held together by INTERmolecular forces (dipole-dipole interactions, London dispersion forces, and hydrogen bonding)

the transition from gas to solid is called

deposition

True or false: The phase diagram for water has a solid/liquid boundary that slants upwards towards the right due to the decrease in density from solid to liquid.

false. Unlike most substances, the phase diagram for water has a solid/liquid boundary that slants up and to the left (instead of right) due to water being less dense in its solid form than in its liquid form.

an increase in entropy is thermodynamically __________

favorable (makes delta G more negative)

covalent solids

held together entirely by intricate covalent networks high m.p. and b.p. extremely hard an example is diamond

Pressure cookers increase the pressure inside of the cooking chamber. This serves to decrease the cooking time dramatically because the higher pressure:

increases the boiling point of water, leading to cooking at higher tempreature The increase in pressure inside of the cooking chamber will raise the boiling point of water. The heat energy that would have been used to transition the water into vapor (i.e. boiling) is then available to be transferred directly to the food, allowing it to cook the food faster.

adhesive forces

intermolecular forces that bind a substance to a surface

cohesive forces

intermolecular forces that bind similar molecules to one another

difference between solids, liquids and gases in terms of compressibility

liquids and solids have fixed volumes gases don't, they are compressible (and expendable)

which phase change leads to increased entropy?

melting vaporization

how to find molecular formula

molar mass/empirical formula mass then determine the common multiplier, or how many times the empirical formula must be repeated

empirical formula is a ratio of

moles of atoms in a sample, not grams

can molecular formula be determined from a sample?

no

phase change depends on (phase diagram)

pressure and temperature

triple point in a phase diagram

represents the temp and pressure in which all three phases are in equilibrium

the transition from solid to gas is called

sublimation

beyond the critical point, the substance becomes

supercritical fluid have low viscosity and high density, giving them properties of both gases and

specific heat capacity

the amount of heat required to raise the temperature of one unit mass of substance by one degree SI unit: J/g·K often used as kJ/kg·K

What is actual yield?

the amount of product actually obtained from a reaction

surface tension

the energy required to increase the surface area of a liquid by a given amount tension created at the liquid's surface by the INTERmolecular forces between molecules

enthalpy of fusion

the enthalpy change that occurs to melt a solid at its melting point

theoretical yield

the maximum amount of product that can be produced from a given amount of reactant It can be calculated

the molecular formula provides information about

the molecular mass or the molecule

capillary action

the movement of a liquid up the sides of a narrow tube against the force of gravity.

what is unique about the phase diagram of water

the solid-liquid boundary slants up to the left, because water is less dense in its solid form. At low temperature, increasing the pressure on ice causes it to melt

critical point in a phase diagram

the terminal point in the liquid-gas boundary line. The temperature and pressure conditions at which beyond the liquid and gas phases become indistinguishable

an increase in enthalpy is thermodynamically ____________

unfavorable, because it increases delta G (more positive)

amorphous solids

A solid made up of particles that are not arranged in a regular pattern

metallic solids

Consist of positive metal ions in the core surrounded by a sea of mobile electrons, hence conduct heat and electricity

heat of vaporization

The amount of energy required for the liquid at its boiling point to become a gas

Two different containers held at standard temperature and pressure are each filled with different compressible gases. If the two containers had equal volumes of gas, What must be true?

The pressure exerted on each container is equal. What differs between the containers would be the number of gas molecules present within each container.