Chem Ch.8

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Chem Ch.8
2010-11-28 12:23:56
chem chapter Thermochemistry heat flow enthalpy

Chemistry Chapter 8 which talks about heat topics in chemistry
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  1. If water in a pot is being heated on a stove, name the system and then the surroundings.
    • System: Water
    • Surroundings: stove, air, pot itself
  2. What is the difference between system and surroundings?
    The system is the part of an action that is most focused on. The surroundings exchange energy with the system, but are insignificant in comparison with the system.
  3. What is needed to define the state of a system?
    mass, temperature, and pressure
  4. What is the basic concept of a state property and give an example of one.
    • A state property is basically a value (or quantity) of something that holds true no mater how that value is reached.
    • Ex: delta(T ) because no matter what temperature you started with the delta(T ) value will still the same
  5. If q is positive, what do you know thermally about a reaction?
    The reaction absorbed heat and the temperature of the solution must have dropped so you know it was endothermic.
  6. What does a calorie equal in Joules?
  7. What is Specific Heat and what are its units?
    • This is the amount of heat energy needed to raise the temperature of one gram of a certain substance by 1oC
    • It's Units are J/g*oC
  8. What is the c of water?
  9. What is the relationship between the heat flow of a reaction and the heat flow of a calorimeter?
  10. Are Heat Capacity and Specific Heat the same?...explain.
    They aren't the same because Specific Heat instead is the amount of heat needed to raise a single gram of the substance 1oC hotter unlike Heat Capacity, which is simply the heat needed to raise something 1oC
  11. What is the name of a type of chemical energy often referred to as "heat content"?
  12. What is the equation to find the change in enthalpy of a reaction?
    q = deltaHreaction = deltaHproducts - deltaHreactants
  13. If after a reaction it is found that deltaH is greater than 0, do you know which of the 2 types of reactions it is?
    It was endothermic
  14. What is the equation called that shows the enthalpy relation between products and reactants?
    Thermochemical Equation
  15. If you find that a reaction of 1 gram of something has a deltaH value of -0.20kJ, what will the enthalpy be of a reaction of 6 grams of that same substance?
  16. What 2 things can be assumed about the products and reactants of a thermochemical equation if they are not specified?
    You would assume the products & reactants are at the same temperature, usually 25oC
  17. If a reaction produces a deltaH of -24kJ, what would its reverse reaction produce in terms of enthalpy, and what would that mean?
    24kJ; this means heat was absorbed
  18. What does Hess's Law (3rd rule of thermochemistry) state?
    Says that the change in enthalpy of a series of reactions is equal to the summation of the change in enthalpy of each step of that reaction.
  19. Summarize the rules of thermochemistry
    • 1) deltaH is directly proportional to amount of reactant or product
    • 2) deltaH changes sign when reaction is reversed
    • 3) deltaH for a series is equal to the sum of deltaH's in that series
  20. What is the meaning behind enthalpy of formation?
    This is the amount of enthalpy change established as true when a compound is formed from the reaction between molecules at a standard pressure (1atm) and a standard temperature (25oC)
  21. What is the universal value for the enthalpy of formation of an element in its stable state?
    0 kJ
  22. How can you calculate the Standard Enthalpy Change (deltaHo)
    The change in standard enthalpy is equal to the summation of the enthalpies of formation of products minus the summation of the enthalpies of formation of the reactants
  23. What is Bond Enthalpy (aka Bond Energy) and what are its units?
    This is known as deltaH when one mole of bonds is broken up in the gaseous state...units are kJ/mole
  24. When is heat always absorbed and when is heat always evolved in terms of chemical bonds of gaseous atoms?
    Heat is always absorbed when bonds are broken, and always given off when bonds are formed.
  25. If there are more bonds in a molecule, will the bond energy for that molecule be greater than if there were fewer bonds?
  26. Are given bond enthalpies for 2 different atoms exact?...and would you want to use them over enthalpies of formation?
    Bond energies for bonds between 2 different elements are the average of values found from different experiments and should not be used over heats of formation.
  27. What is the thermodynamic definition of work?
    Work is all forms of energy other than heat
  28. What does the First Law of Thermodynamics say and what is the equation for it?
    • Says that the total change in energy of a system is equal to the sum of the heat (q) and work (w) transferred between the system and surroundings.
    • deltaE = q + w
  29. What are the equations denoting:
    Change in enthalpy at a constant pressure?
    Change in energy at a constant volume?
    • deltaH = qp (qp is heat flow at constant pressure)
    • deltaE = qv (qv is heat flow at constant volume)
  30. What are the 3 derived equations that relate enthalpy to energy?
    • H = E + PV
    • deltaH = deltaE + deltaPV
    • deltaH = deltaE + (delta ng)RT