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.