Chem32 Chapter 4.txt

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Chem32 Chapter 4.txt
2011-10-02 17:52:20
pressure liquid gas solid state phase thermal energy

Chem32 Chapter 4
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  1. What is energy.
    Energy is the ability to do work. If an object can do work then it has energy.
  2. What is work?
    Work is any movement of matter against a resistance.
  3. What is kinetic energy?
    Energy of motion. An object with mass moving at a velocity has energy of motion and can do work.
  4. What is potential energy?
    Stored energy. An object with mass that is not in its most stable position has potential energy. Any object up off the ground has potential energy due to the fact that gravity is trying to pull it to the ground.
  5. What is the law of conservation of energy?
    Energy cannot be created or destroyed. It can be transfered, coverted into different forms, but can not be destroyed or created.
  6. What is thermal energy?
    The random, kinetic energy of atoms.

    Atoms of any substance are always moving around rapidly and randomly. This constant, rapid motion generates heat. The relationship between the speed of the atoms, the amount of energy, and the -temperature- of a substance is where the name "thermal" comes from.

    The faster the atoms move, the more energy the substance has, and the warmer the substance will be.

    The more something is heated, the faster its atoms move, and the more energy it has.
  7. What is heat?
    Heat is the amount of thermal energy that is added to or removed from a substance.

    heat = mass x change in temperature x specific heat
  8. What is specific heat?
    Specific heat is the amount of energy required to change the temperature of one gram of a substance by one degree Celcius.
  9. What is a calorie?
    A calorie is a measurment of energy.

    • 1 cal = 4.184 joules
    • 1 joule = .239 cal

    • 1 kcal = 1000 cal
    • 1 cal = .001 kcal
  10. How to calculate how much energy is needed to change temperature of something by a certain amount?
    How much energy is needed to change 250g water ( cp 1/1 ) by 30 degrees C?

    250g x 30C x 1/1 ( 1 ) or 250 x 30 x 1 = 7500cal

    How about 75g ethyl alcohol ( cp .58 ) by 25C

    75g x 25 x .58/1 or 75 x 25 x .58 = 217.5cal
  11. What are three main characteristics of a solid?
    Fixed shape - holds its shape in a container, a square solid remains square when put in a round container.

    Fixed volume - 1 cubic centimeter of a solid will take up 1 cubic centimeter of space when released from its 1 xubic centimeter container.

    Density - moderate to high.
  12. What are three main characteristics of a liquid?
    Variable shape - liquids take on the shape of their containers.

    Fixed volume - 1 cubic cm of a liquid will take up 1cubic cm of space when released from its 1cubic cm container.

    Density - moderate to high.
  13. What are three main characteristics of a gas?
    Shape - gases really don't have a shape, it changes.

    Volume - an amount of gas can take up a lot or a little space.

    Density - very not dense at all.
  14. How do atoms in a solid behave?
    Atoms in a solid are packed very close to each other and cannot move around but stay in one fixed place, vibrating. Because atoms in a solid are so close to each other solids cannot contract. Strong bonds between the atoms prevent the solid from expanding easily, too.
  15. How do atoms in a liquid behave?
    Atoms in a liquid are closely packed in to one another so liquids can't contract or expand very well. Since the bonds between atoms in a liquid are not as strong as those in a solid, the atoms remain in contact with each other but can move about in the sample.
  16. How do atoms in a gas behave?
    Atoms in a gas are not packed in tightly as in a liquid or solid and in fact are not in contact with one another. They are mostly empty space. Because of this gasses can expand and contract very easily.
  17. What is the relationship between thermal energy, speed of atoms, and temperature of a substance?
    A substance is; a solid, has the slowest speed of atoms, and lowest thermal energy at its lowest tempwerature.

    A gas when the speed of its atoms are fastest, its temperature its highest, and thermal energy is its highest.

    A liquid when its speed of atoms, temperature, and thermal energy are all median.
  18. What is pressure?
    Pressure is force divided by area. For a given force, pressure is greater for a smaller area and less for a small area.

    • force
    • pressure = -------------
    • area
  19. What is psi?
    Pounds per Square Inch. One pound of force over 1 square inch = 1psi.
  20. What is torr?
    Torr is unit of pressure used in medicine to measure blood pressure or gas pressure.

    • 1 torr = .019 psi
    • 1 psi = 51.7 torr
  21. What is a bar?
    Unit of pressure.

    • 1 bar = 750 torr
    • 1 bar = 14.25 psi
  22. What is an atm (atmosphere)?
    Unit of pressure.

    • 1 atm = 760 torr
    • 1 atm = 14.7 psi
  23. How can you increase the pressure of a gas in a container?
    1. Increase the number of atoms - Part of the pressure on the container is the number of atoms hitting the inside walls of tbhe container. Increasing the number of atoms increases the number of collisions and the pressure itself.

    2. Increase the speed of the atoms by heating the gas - Part of the pressure on the container is the speed at which the atoms hit the sides of the container. Heating the gas will cause the atoms to move faster (increased thermal energy) and hit the walls harder.

    3. Decrease the size of the container - Pressure is force divided by area. With a smaller container there is a smaller area and the pressure greater.
  24. What is partial pressure?
    A gasseous mixture of different gasses will have a certain pressure. Each gas will exert an amount of pressure related to its portion of the whole mixture.

    If a container holds 30% Bromine and 70% Chlorine then the bromine is responsible for 30% of the pressure and chlorine is responsible for 70% of the pressure in the container. 3ach portion of the pressure is a -partial pressure-.
  25. What is Dalton's Law of Partial Pressure?
    The partial pressures of the gasses in any mixture add up to the total pressure of of the gas mixture.
  26. What is condensation?
    Matter changing from gasseous to liquid state.

    The thermal energy, temperature, and speed of atoms of the substance all decrease.
  27. What is evaporiation?
    Matter changing from liquid to gasseous state.

    When matter has changed from liquid to gas its temperature, thermal energy, and speed of atoms all increase.
  28. What is sublimination?
    When matter changes from solid directly to gas.

    When the matter changes to gas its temperature, thermal energy, and speed of atoms all increase.
  29. What is melting point?
    The temperature at which a solid melts.
  30. What is boiling point?
    The temperature at which a liquid boils.
  31. What is freezing point?
    The point at which a liquid freezes and becomes a solid.
  32. How does pressure affect boiling point?
    The lower the pressure the lower the boiling point of a substance.

    The higher the pressure the higher the boiling point.
  33. What is heat of fusion?
    The amount of heat needed to melt one gram of a solid.

    • The heat of fusion of ice is 80 g/cal.
    • To melt 15 g of ice you need ( 15g x 80cal ) = 1200 calories of heat.
  34. What is heat of vaporization?
    The amount of heat required to boil one gram of aliquid.

    The heat of vaporization of water is 540 calories.

    To boil 25 grams of water it takes ( 15 x 540 ) = 8100 calories of heat.
  35. What is a heating curve?
    A graph of temperature against heating time. There are five steps to it.

    • 1. Solid heats up to melting point.
    • 2. Solid melts.
    • 3. Liquid heats up to boiling point.
    • 4. Liquid boils.
    • 5. Liquid heats up further and becomes gas.
  36. What happens to the atoms of a substance as it heats up?
    The atoms tend to move away from one another.
  37. What is the attraction between two oppositely charged ions called?
    Ion-ion attraction.

    It is a very strong attraction.
  38. What is an ion-ion attraction?
    The attraction between two oppositely charged ions.

    It is a very strong attraction.
  39. What do all room-temperature ionic compounds have in common?
    They are all solids.

    All ionic compounds are solids at room-temperature.
  40. Which is stronger, the attraction between molecules or the attraction between ions?
    The attraction between ions is stronger.
  41. What is dispersion force?
    Dispersion force is the attraction between all molecules.

    All molecules have electrons and protons. The electrons of molecules will always be attracted to the the protons of nearby molecules.

    Atoms of different elements have different masses. Large molecules ( made of many atoms or of very large atoms ) have more electrons and protons and a greater attraction for other nearby molecules, a greater dispersion force.

    A substance made up of larger molecules will have a stronger bond between molecules and thus a higher melting point. Since the bond between molecules is stronger it will take more heat/energy to pull the molecules apart.
  42. What is dipole-dipole attraction?
    The attraction between to molecules with polar bonds.

    A molecule with a polar bond ( a covalent bond between two atoms with very different electronegativities ) leaves one of the atoms positively charged and the other negatively charged.

    The positive or negative charge of these atoms makes them slightly more attractive to other molecules with atoms charged due to polar bonding.
  43. What is a hydrogen bond?
    Attraction between a positively charged (H)ydrogen atom and a negatively charged (O)xygen or (N)itrogen atom.

    **Only Hydrogen atoms covalently bonded to Nitrogen or Oxygen atoms can participate in hydrogen bonds.
  44. What is a solution?
    A homogeneous mixture of two or more substances. ( usually a liquid )

    The solvent is the major, usually liquid part and the solute, "the other stuff". When a solute dissolves in a solvent its mollecules become evenly distrbuted throughout the solution.
  45. What is a solvent?
    The liquid part of a solution ( if the solution contains only one liquid ).

    In a sugar water solution water would be the solvent and sugar would be the solute.
  46. What is a solute?
    "all the other stuff" in a solution that is not the solvent. The solvent is usually the liquid and the solute "the other stuff".

    In a sugar water solution water would be the solvent and sugar would be the solute.

    Solutes can be solids, liquids, gasses.
  47. What is an aqueous solution?
    A solution that contains water.
  48. What is a suspension?
    A heterogeneous mixture of two or more substances ( usually a solid and liquid ) in which you can see a distinction between the two substances.
  49. What is a colloid?
    A mixture that appears to be a solution ( homogeneous mixture ) but has very large molecules or clusters of ions still stuck to each other.

    Shining a beam of light through a colloid will show the light reflecting off the large molecules or chunks of ions.
  50. What is one way you tell if a compound will dissolve in water?
    If the compound has hydrogen bonds ( n-h, o-h ) then the compound will dissolve in water.

    The water molecules will break from each other and bond with the o-h or o-n molecules of the substance.

    H2O will have one negatively charged Oxygen and two positively charged Hydrogen atoms, normally all stuck to each other as a liquid.

    If a substance with o-h or n-h bonds is introduced into water then the molecules of the substance break apart from each other, the molecules of water break apart from each other and the negative Os of the water molecules attract to the positive Hs of the substance molecules.

    Or, the positive Hs of the water molecules bond with the negative Os or Ns of the substance molecules.
  51. What is a hydrogen bond donor?
    The molecule that supplies the positively charged Hydrogen atom in a hydrogen bond ( attraction ).
  52. What is a hydrogen bond acceptor?
    The molecule that has the negatively charged N or O atom that -accepts- the Hydrogen atom.
  53. Can molecules that have Nitrogen or Oxygen atoms not bound to hydrogen participate in hydrogen bonding?
    Yep. :)

    If an Oxygen or Nitrogen atom is involved in a covalent bond on a molecule then it is going to have more electrons then it started with and will be negatively charged.

    Many molecules with such negatively charged N or O atoms can participate in hydrogen bonding by being a hydrogen acceptor.
  54. Can a molecular substance that cannot participate in hydrogen bonds dissolve in water?
    Usually not.

    The bonds between the water molecules will be very strong and the water molecules will prefer to stay stuck to each other rather that molecules of the substance.
  55. What is an electrolyte?
    A chemical compound that conducts electricity when it dissolves in water.

    The chemical compound must form ions when broken down in water for it to be an electrolyte. This will mostly be ionic compounds, NaCl for example.

    When introduced to water the water molecules break apart from each other and the positively charged Hs pull the negative ions and the negatively charged Os pull the positively charged ions apart from each other ( with a terrible ripping sound ), this is dissociation.

    The water molecules then surround and isolate the separated ions. This is solvation.
  56. What is dissociation?
    The process wherein ionic compounds are broken apart into separate ions.
  57. What is solvation?
    The process in which after an ionic compound is broken down into separate ions the separate ions are surrounded by water molecules.
  58. What happens to an ionic compound made with 2 or more of the same ion when it dissolves in water?
    When such an ionic compound, like MgCl2, dissociates in water the 2 Cl separate and break into two Cl- ions and the 1 Mg breaks off into one Mg2+ ion. The two Cl are both negatively charged and repel rather than stick to one another.
  59. What happens to a polyatomic ionic compound in water?
    In short, the polyatomic ion acts as a single ion and stays intact.
  60. What is special about ionic compounds that contain Na+ or K+?
    All ionic compounds that contain these ions will dissolve in water.
  61. What is solubility?
    Solubility of a substance is the largest amount of substance that will dissolve in a liter of water before no more will dissolve.

    Solubility of salt ( NaCl ) is 360g/L. 360 grams of salt will dissolve in a liter of water but no more.
  62. What is an unsaturated solution?
    A solution in which the solute has not reached its solubility. Meaning you could still add a little more of the solute and it would dissolve.
  63. What is a saturated solution?
    A solution in which the solute has reached its solubility and no more of it will dissolve in the solvent. Meaning, if you added more of the solute it would not dissolve.
  64. What is soluble?
    If a substance has a solubility of at least 10g/L or higher.
  65. What is insoluble?
    If the solubility of a substance is 1g/L or less.
  66. The solubility of a solid in water increases as temperature...
  67. The solubility of a gas in water increases as temperature...
    goes down.
  68. The solubility of a gas in water increases as pressure...
  69. On molecules and their ability to dissolve in water...
    The more hydrogen bonds a molecule can form, the more soluble it is in water.

    The more hydrogen and carbon atoms a molecule has, the less soluble it is in water.

    If it is a very large molecule with only one hydrogen acceptor or donator then there isn't enough of it that can bond with water for it to dissolve.

    If the molecule has many H and C atoms, as some molecules do, there is less of a chance it will dissolve.