Chem Test Ch.12
What is the lowest temperature liquid CO2 may exist
-56.4 degrees C
What is Carbon dioxides normal boiling point? What phase change takes place at this temperature?
-78.5 degrees C 1 atm
List the four types of crystals and give brief descirption
1. covalent network- large # of atoms covalently bonded to one another. Melt at a high temp and tend to be nonconductors or semiconductors. 2. metallic- crystals have metal cations surrounded by a sea of delocalized valence electrons and are good conductors. 3. ionic- most brittle, have regular arrangement of charged particles. Melt at a high temp. Good insulators. 4. covalent molecular- have IMF have a low melting point. Good insulators.
In which phase of matter do particles move the quickest?
Plasma has the most energetic particles.
How does a pressure cooker work? Why is it harder to cook foods by boiling them at high altitudes
Pressure cookers work by increasing the pressure in the pot thus raising the equilibrium vapor pressure and thusly increase the boiling point. This allows the food to cook at a higher temperature. It is hard to cook foods by boiling them at high altitudes because the air pressure is lower at high altitudes.
What is the least compressible phase of matter? Why?
Solid because the particles are insanely close and packed together
Why is a water molecule polar?
Water is polar because the oxygen molecule has a higher electronegativity and holds onto the electrons it shares with hydrogen more. This unequal sharing causes the oxygen end of the molecule to appear as if it has a negative charge (Partial negative - d -) Conversely the hydrogen side appears to have a partial positive charge (d +).
State Le Chatlier's Principle
When a system in equilibrium undergoes a stress, the system will attain a new equilibrium position that minimizes stress. When it leaves equil it tries its best to get back.
What will happen to the vapor concentration, and number of molecules in a closed system at equilibrium if its volume is increased? What will happen to the rates of condensation and evaporation?
When the volume increases the vapor concentration is decreased. (Same amount of material in a bigger space.) The rate of condensation is dependent on the vapor concentration and will consequently decrease. Because of the imbalance the vapor concentration will recover to its original amount and re-establish equilibrium at the same rate. The rate of vaporization is not changed because temp is not change. The net result is an increase of vapor molecules and decrease in liquid. The vapor pressure will dip but quickly recover to its original value.
Which of the 4 types of crystals has the lowest melting point.
covalent molecular has the lowest melting point because of the weak IMF.
What does the line that connects Y and X represent in the phase diagram for water?
equilibrium between a gas and a solid
What does the line that connects A and D represent in the phase diagram for water
equilibrium between a liquid and a gas
What does the line that connects A and B represent in the phase diagram for water?
equilibrium between a solid and a liquid
What will happen if H2O is present at its triple point and you increase the pressure
it forms a liquid
What will happen if CO2 is present at its triple point and you increase the pressure?
it forms a solid
What property of a liquid is responsible for surface tension?
the force that holds the atoms together--> because of the unequal forces. Cohesive force.
Define equilibrium. Give an example of a non-chemical system that exists in equilibrium.
when two opposing processes happen at equal rates. hockey game, bank account
Describe the energy changes involved as ice is brought through a temp range of -2 degrees C to 110 degrees C at normal atmospheric pressure. Indicate what is happening with both KE and PE.
As the ice raises temp from -2 to 0 it is gaining KE (temp increases. At 0 it melts and increases PE and its particles are brought closer together (no change in temp), from 0 after completely melting the temp will begin to rise as it again increases KE until it reaches 100. The water will remain at 100 until it all boils and turns to steam. There is no change in KE but PE increases as particles spread. From 100 to 110 the KE increases as the temp does.
Define boiling and explain how it differs from evaporation
Boiling only occurs when the equilibrium vapor pressure is equal to the atmospheric pressure or system pressure. Evaporation, on the other hand, occurs at any temperature due to random energy or particles near the surface of a liquid. If the particle happens to have enough energy and is at the surface it may get free of the liquid.
How do amorphous solids differ from crystalline solids?
Crystalline solids atoms have a geometric pattern while amorphous doesn't.
Why does it feel colder out when your skin is wet?
Evaporation of sweat from the skin surface has a cooling effect due to the latent heat of evaporation of water Basically, the heat is transferred from your skin to the water, the water then evaporates, taking with it a bit of the energy stored in it.
Why does ice float? Describe the difference between water and ice in terms of molecular arrangement.
Ice floats because, unlike most materials it expands as it freezes. Because it expands, it becomes less dense and thus floats. The reason ice is less dense is because of the geometric pattern that is produce from several hydrogen bonds formed between molecules of water in the solid phase.
Which of the 4 types of crystals is the most brittle
Ionic is the most brittle because if you break the pattern and put positives with positives it will shatter.
List the names of the 5 types of phase changes and show what phase is changing to what
Melting: solid to liquid Freezing: liquid to solid Vaporization: liquid to gas Condensation: gas to liquid Sublimation: solid to gas deposition: gas to solid
What factors affect the equilibrium of a liquid/vapor system?
Temperature, surface area, and Vapor concentration
Define critical point
The critical point is the point on a phase diagram at which any temperature higher must be in the gaseous state.
Define the molar heat of fusion and the molar heat of vaporization
The molar heat of fusion is the heat needed to melt one mole of a substance. The molar heat of vaporization is the heat needed to vaporize one mole of a liquid.
Define normal boiling point
The normal boiling point and melting points are the temperatures at which a substance will boil or melt at normal atmospheric pressure (1 atm).
Why will a slightly porous canvas bag keep water cool?
The porous bag allows water to seep out slowly and as the surface gets wet the water begins to evaporate. As it evaporates it absorbs heat from the water thus keeping it cool.
What is meant by equilibrium vapor pressure
The pressure exerted by the molecules of a vapor which is in equilibrium with its corresponding liquid at a given temperature.
Why do liquid propane cylinders register fairly consistent pressure until almost empty
The propane is dependent on the vapor concentration. The concentration does not change because as gas is released the rate of condensation decreases (due to less vapor) until the vapor concentration is restored by the imbalance. When all the liquid is used up the pressure will drop according to Boyle's Law
Predict what will happen to the following if a system that is in equilibrium has its temperature raised 10 degrees. rate of condensation; rate of evaporation; final concentration of vapor; final number of liquid molecules.
The rate of vaporization is dependent on the temperature and therefore will increase. This increase will cause an increase of vapor molecules and vapor concentration. Because the rate of condensation is dependent on vapor concentration the rate of condensation will increase and equilibrium will be re-established at the higher temperature. The net effect will be an increase in vapor molecules and vapor pressure. Because the vapor concentration increases the number of liquid molecules must be decreased.
Define triple point
The triple point is the pressure and temperature conditions where all three phases may exist in equilibrium.
