# chem chapter 6

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1. Thermodynamics
is the science of the relationships between heat and other forms of energy
2. thermochemistry
the study of the quantity of heat absorbed or evolved by chemical reactions
3. Energy
• the potential or capacity to move matter
• property of matter
• exists in different forms that can be interconverted
• can not be created no destroyed
4. kinetic energy
is the energy associated with an object by virtue of its motion
5. formula for kinetic energy
Ek=1/2 mv^2

• ek kinetic energy (joules)
• m mass in kg
• v velocity in m/s
6. calorie (cal)
non SI unit of energy commonly used by chemists originally defined as the amount of energy required to raise the temperature of one gram of water by one degree Celsius
7. one cal = _______ joules
4.184
8. potential energy
the energy an object has by virtue of its position in a field of force
9. formula for potential energy
Ep=mgh

• Ep - potential energy j
• m- mass kg
• g - acceleration due to gravity m/s
• h - height (m) measured from a standard level -- the surface of the earth
10. internal energy (U)
the sum of the kinetic and potential energies of the particles making up a substance
11. equation for total energy
Etot= Ep + Ek + U
12. Law of conservation of energy
energy may be converted from one form to another but the total quantity of energy remains constant
13. thermodynamic system
the substance or mixture of substances under study in which a change occurs
14. surroundings
everything in the vicinity of the thermodynamic system
15. heat
the energy that flows into or out of a system because of a difference in temperature between the thermodynamic system and its surroundings
16. thermo-equilibrium
as long as the system and the surroundings are not insulated from one another energy heat flows between them to establish an equilibrium
17. heat flows from
higher temperature region to a lower temperature region
18. temperature
proportional to kinetic energy
19. heat q
the symbol for heat is denoted by q
20. q is positive when
heat is absorbed by the system
21. q is negative when
heat is evolved by the system
22. heat of reaction
is the value of q required to return a system to the given temperature at the completion of the reaction
23. exothermic
is a chemical reaction or a physical change in which heat is evolved and q is negative (reaction vessel warms)
24. endothermic
is a chemical reaction or a physical change in which heat is absorbed and q is positive (reaction vessel cools)
25. enthalpy
• denoted H is an extensive property of a substance that can be used to obtain the heat absorbed or evolved in a chemical reaction
• state function
26. state function
a property of a system that depends only on its present state which is determined by variables such as temperature and pressure and is independent of any previous history of the system
27. change in enthalpy = enthalpy of reaction (delta H)
• the change in enthalpy for a reaction at a given temperature and pressure
• delta H = H(products) - H (reactants)
28. the enthalpy of reaction equals
• the heat of reaction at constant pressure
• deltaH = qp
29. relationship between enthalpy and internal energy
H=U+PV

• H the enthalpy
• U internal energy
• P pressure
• V volume
30. Thermochemical equations
• the chemical equation for a reaction including phase labels in which the equation is given a molar interpretation and the enthalpy of reaction for these molar amounts is written directly after the equations
31. rules when manipulating thermochemical equations
1. when a thermochemical equation is multiplied by any factor the value of delta h for the new equation is obtained by multiplying the value of delta h in the original equation by that same factor

2. when the chemical equation is reversed the value of delta h is reversed in sign
32. converting from grams to kilojoules of heat
(grams of A) X (conversion factor: g A to mol A using molar mass) X (conversion factor mol A to kJ using enthalpy of reaction) -> kilojoules of heat
33. heat capacity (C)
the heat required to raise the temperature of a substance one degree Celsius or one kelvin

q=CdeltaT
34. specific heat
the quantity of heat required to raise the temperature of one gram substance by one degree Celsius or kelvin at constant pressure

q=mCdeltaT
35. calorimeter
a device used to measure the heat absorbed or evolved during a physical or chemical change

for reactions involving gases a bomb calorimeter is generally used
36. Hess's law
for a chemical equation that can be written as the sum of two or more steps the enthalpy change for the overall equation equals the sum of the enthalpy changes for the individual steps
37. standard state
• the standard thermodynamic conditions chosen for substances when listing or comparing thermodynamic  data :
• 1atm pressure and 25 degrees celcius -- 298 k

conditions denoted by ()
38. allotrope
one of two or more distinct forms of an element in the same physical state
39. the reference form
the stablest form of the element under standard thermodynamic conditions
40. standard enthalpy of formation/standard heat formation
deltaHf

is the enthalpy change for the formation of one mole of the substance in its standard state from its elements in their reference form and in their standard states
 Author: alazeidan ID: 260504 Card Set: chem chapter 6 Updated: 2014-02-06 04:00:33 Tags: chem Folders: chem Description: chem Show Answers: