Unit 2 Flashcards
Humans an other living things are composed of
carbon, hydrogen, nitrogen, phosphorus, and sulfur
All matter can be broadly classified two ways
Puré substances and mixtures
Pure substances
A substance that has a fixed chemical composition throughout is called a pure substance
Can be elements or compounds
Ex. Water, oxygen gas, ammonia
Mixtures
composed of two or more pure substances that retain their own physical and chemical properties
Further classified as heterogenous or homogenous
Homogeneous mixture
Has a consistent composition where you are unable to distinguish the separate components from each other can be separated by physical means, i.e. filtration, distillation, evaporation, etc.
Heterogenous mixtures
Not a consistent composition and the components can be distinguished from each other
can be separated by physical means, i.e. filtration, distillation, evaporation, etc.
Colloids are
Homogenous mixtures
Suspensions are
Heterogeneous mixtures
Sublimation
Solid to gas
Deposition
Gas to solid
Particles of solids and liquids are held together by intermolecular forces. Gases have particles that have virtually no interactions with each other and completely fill the volume of a container that they are held in.
Physical properties
can be measured and observed without changing the identity of the substance.
Chemical properties
can only be observed when a chemical reaction occurs. Chemical properties describe the reactivity of a substance with other substances and its ability to change into a new substance. Chemical properties also describe a substance’s chemical composition (the type and number of atoms) and reactivity, or how it behaves when in the proximity of other substances.
Evidence that a chemical change has occurred
includes a change in color, the formation of bubbles, a solid precipitate forms, or heat is absorbed or released which can be measured by a change in temperature. Temperature changes can also accompany physical changes such as dissolution or phase changes.
All chemical changes are accompanied by a
Physical change
Delta symbol in reactions
Used to show heat is needed
energy
Ability to do work or supply heat.
Two major forms of energy are potential and kinetic energy. Potential energy is stored energy while kinetic energy is the energy of motion.
Light is a type of
electromagnetic radiation and makes up a very small portion of the electromagnetic scale.
Light also gives off heat, hence when you stand in the sunshine on a sunny day you can feel the heat from the sun; whereas standing in the shade, not in direct sunlight, is cooler.
Heat
the flow of kinetic energy from a warmer object to a cooler object.
Kinetic energy
Warmth is a measure of the amount of kinetic energy that a substance has.
The more kinetic energy, the more “heat” a substance has. Cooler objects have less kinetic energy than warmer ones.
Heat is transferred as warmer particles bump into cooler particles—as they touch, the kinetic energy of one particle is transferred to the next particle and so on.
temperature
Measure of the average kinetic energy that a substance has
Temperature
measure of the average kinetic energy of a substance. Temperature can be measured using a thermometer.
Celsius and Kelvin conversion
C = K – 273
K = °C +273
Kelvin and Celsius
temperature at which water freezes or its melting point is 0°C and 273.15 K while the boiling point of water is 100°C and 373.15 K.
Melting and boiling point Fahrenheit
The melting point of water on the Fahrenheit scale is 32°F and the boing point is 212°F.
Fahrenheit and Celsius conversion
°F = (1.8 x °C) + 32
°C = (°F - 32)/1.8
Energy units
1 cal = 4.184 J
1 kcal = 4184 J
1 Cal = 1 kcal = 1000 cal
1 kJ = 1000 J
Specific heat
(the amount of energy required to raise the temperature of 1g of a substance by one Celsius degree)
the higher the specific heat, the more energy that is required to raise the temperature of that substance.
Water specific heat
(1 cal /1 g·°C or 4.184 J/1 g·°C)
Large amount of heat energy must be absorbed to increase the temperature; in turn, large amounts of heat must be lost from water to decrease its temperature
Specific Heat for pure substances:
SH = heat/g ·ΔT (where ΔT is the change in temperature = T final - T initial
Units: cal/1 g·°C (metric system)
Or
J/1 g·°C (SI System)
For water:
SH = 1 cal/1 g·°C = 4.184J/1 g·°C
calculate the amount of heat that is added or lost from a pure substance using the following equation
Q = mcΔT equation 2.1
Q = heat lost or gained
m = mass of the substance
c= specific heat of the substance
Delta T: change in temp (final - initial temp)
A negative value for Q simply means that heat is lost (there are no negative values for energy)
Therefore, if heat is lost ΔT is (-), and Q will be a (-) number and when heat is gained ΔT is (+) and Q will be a (+) number. Thus the (+) or (-) sign for Q only indicates whether heat is lost (-) or gained (+).
heat of vaporization
energy required to completely convert a liquid sample to a gas, at the boiling point
Boiling point of a substance is
The temperature at which the vapor pressure of a substance equals the surrounding atmospheric pressure
Vapor pressure of a liquid
The vapor pressure of a liquid is the pressure exerted by its vapor above the liquid on its container
The vapor pressure is inversely related to the strength of the intermolecular forces holding individual particles together in the liquid state
The stronger the forces holding the particles together, the lower the vapor pressure of a substance
Substance with high vapor pressure has low BP ex. (Indirect relation)
As a temp of a substance increases, the vapor pressure increases ex. (Direct relation)
a substance with a high vapor pressure
will boil at a lower temperature than a substance that has a lower vapor pressure.
[IMF]
Ion-ion
Strongest IMF
Large ionic solids held together by these networks of ionic bonds
(Both have charges +,-)
Formal charges
[IMF]
Ion-dipole
Formal charge and partial charge
[IMF]
Dipole-dipole
Partial charges
[IMF]
Van der Waals
London dispersion
Induced dipoles
Everyone has
latent heat of fusion
-amount of heat energy absorbed to melt a substance
-The heat of fusion is lost when a liquid freezes into a solid
latent heat of vaporization
amount of heat energy absorbed to cause a liquid to boil
the heat of vaporization is lost when a gas condenses to a liquid
heating curve
graphs the amount of heat energy vs. the temperature of a substances as it undergoes phase changes from a solid to a gas
-The reverse processes can be observed using a cooling curve. -Notice that at the melting and boiling points the temperature does not change on the graph.
For a given amount of a substance, the heat released during freezing is
Equal to heat absorbed during melting, it is called the heat of fusion and the temp stays the same during the process
Equation for energy change
Delta H
During change in temp
Delta T
Delta H = m x Cphase x Delta T
Mass of substance x specific heat of each phase (solid, liquid, gas) x temp change
Equation for energy change
Delta H
During a phase change
Delta H = DeltaHdeltaphase x #mols
DeltaHdeltaphase = heat of phase change (energy required for one ole of a sub to change from one phase to another)
Physical properties
Size, color, temp MP, BP etc
Chemical properties
Chemical composition: what matter is made of
Chemical reactivity: how matter behaves
Observed when chemical reaction occurs
Describes ability of substance to interact w other substances or change into a new substance
When adding T or subtracting T
Use addition and subtraction decimal rule for SFs
MP = FP
BP = CP
Enthalpy (heat)
Entropy (disorder)
-enthalpy change ΔH – measure of the heat absorbed or released during a process.
– entropy change ΔS – measure of the change in molecular disorder or freedom that occurs during a process.
Solid to liquid and liquid to gas
Heat is absorbed endothermic ΔH is positive (+) and entropy increases
Gas to liquid and liquid to solid heat is lost exothermic ΔH is negative (-).
Entropy decreases
Evaporate
Molecules on the surface gain sufficient energy to form a gas
Condense
When gas molecules lose energy and form a liquid
– The heat of fusion (for melting)
– The heat of vaporization (for boiling)
Vapor pressure
Unique for pure substances
is the partial pressure of vapor molecules in equilibrium with a liquid.
Water specific heat
4.184 J/gC
Or
1 cal/gC
