Chem: Thermochemistry

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54 Terms

1
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Define Thermochemistry

the study of energy changes that occur during a chemical reaction and changes in the state

2
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Define energy

the ability to work or produce heat

3
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Define temperature

a measure of the amount of kinetic energy an object/substance has

measured in C or K

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Define Heat

thermal energy- energy that transfers from one object to another

measured in joules (q)

transfers because of difference in temperature

always flows from a warmer temperature to a cooler object

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Which would have more thermal energy?

The one with more of a substance because it has more to transfer to

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Potential Energy

stored energy that could be used

- gravitational: ball on top of a hill

- elastic: stretching a rubber band

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Kinetic energy

the motion of an object

KE= 1/2 mv^2

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Law of conservation of energy

energy can neither be created or destroyed

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chemical potential energy

energy thats stored in the chemical bonds of a substance

determined by types of atoms and their arrangement

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System

the reaction or focus

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surroundings

everything around the reaction

ie. container, room, etc.

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universe

system and surroundings

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define exothermic process

heat is released into the surroundings by the system

exo = exit

-q

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define endothermic process

heat is absorbed from the surroundings by the system

endo = in

+q

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what are the 2 common units for energy?

joules

calories

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how many joules are in 1 calorie?

4.184 J = 1 calorie

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How many calories in 4.184 J?

1 calorie = 4.184 J

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How many calories are in 1 kilo calorie?

1000 calories = 1 kilo calorie

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How many calories are in 1000 calories?

1 kilo calorie = 1000 calories

20
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define heat capacity

amount of heat needed to increase the temperature of an object by 1'C

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heat capacity depends on:

mass of an object

chemical composition of the object

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define specific heat capacity

amount of heat needed to raise the temperature of 1g of a substance by 1'C

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specific heat capacity of water

4.184 J/g'C

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define molar heat capacity

amount of heat needed to raise the temperature of 1 mole of a substance by 1'C

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what does each letter represent?

q=MCAT

q- heat

m- mass

c- specific heat

AT- change in temperature (final - initial)

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what does -q mean compared to q?

-q heat loss

q heat gain

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define calorimity

precise measurement of heat flow into and out a system

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heat released by the system = ?

proved by law of conservation of energy

heat released by the system = heat absorbed by the surroundings

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define calorimiter

insulated device used to measure absorption or release of heat

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final temp of system = ?

final temp of system = final temp of the surrondings

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define enthalpy

the heat constant of a system at constant pressure

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AH

heat of a reaction

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q system

q surrondings

q system

q system- AH

q surrondings- MCAT

q system- AH= -qsurrondings = -MCAT

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negative enthaply means..

exothermic

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positive enthalpy means...

endothermic

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how to write enthaply in thermochemical equations

the heat change can be written as a reactant or product

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define molar Heat of fusion

heta absorbed by one mole of a solid substance when it melts at a constant temperature

AH(fus)

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define molar heat of solidification

heat lost by one mole of a liquid substance when it solidifies

AH(fus) = -AH (solid)

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what does the graph look like when a phase change is occurring?

plateau

40
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define molar heat of vaporization

heat energy required to boil one mole of a substance at its boiling point

AH(vap)

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defien heat of a solution

enthaply change caused by dissolution of 1 mole of a substance

AH(sol)

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heat_of_fusion_number

6.02

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heat_of_vaporization_number

40.7

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define_hess's_law

if_you_can_add_two_thermochemical_equations_to_produce_a_final_equation,_the_sum_of_the_enthaply_of_those_equals_the_enthalpy_of_the_others

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condensing_steam

exo

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burning_alcohol

exo

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evaporating_alcohol

endo

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baking_potatoes

endo

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how_to_find_molar_heat_capacity

use the specific heat to convert it to moles with grams on top

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triangle H means what?

heat of formation

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standered conditions are what?

25'C and 1atm

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difference between calorie, specific heat, and molar heat

specific heat- 1g

calorie- 1g of water

molar heat- 1 mole

53
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condensing

exothermic

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C

nutrional calories