Thermochemistry
Where does heat come from?
Specific heat

Every object absorbs and loses heat at
different rates.

If you gain/lose heat easily, you have a
_____ specific heat

If its difficult to gain/lose heat, you have
a _____ specific heat

Specific heat of water is 4.184 J/goC

Usually occur on their
own

They give off ______ (q)

q (or ∆H) is __________

Bonds are formed

Heat is a product
Na(s) + 0.5Cl2(s)  NaCl(s)

need heat to get started

Feels ______ to the touch

They need energy from
heat to react

q (or ∆H) is __________

Bonds are broken

Heat is a reactant
6CO2(g) + H2O(l)  C6H12O6(aq) + 6O2(g)
 What
reaction is this???
q
= heat = ∆H
 If we can calculate q, then we will know
if the reaction is endo or exothermic
 If +q  _____________
 If –q  _____________
heat
mass
specific heat
capacity
temp.
Tf - Ti = ∆T
Specific heat is the amount
of energy it takes to increase
the temperature of 1g of a
substance by 1oC
 Example:
if the temp of a reaction with water
changes from 5oC to 25oC, what is the
heat of the reaction when we start with
10g of water? (Cwater = 4.18 J/goC )
A
calorimeter is a container that
measures the change in __________
without being affected by _____________.
 The calorimeter is acting as the ________.
 The reaction always has the _________
sign than the surroundings
 qsurroundings = -qreaction
 Energy
is never lost or destroyed (law of
_____________of energy)
 There are 2 different ways heat energy
can be passed…
Conduction
– the movement of heat by
_______with another source
Convection
– the movement of heat
through the _____
Which graph do you think represents
endothermic rxns?
exothermic rxns?
Usually builds bonds
Usually breaks bonds
Energy

Measured in Joules

Several different types
 Thermal
 Kinetic
 Chemical
 Potential
Practice…

If 84 g of water at 22oC are mixed
with 150 g of ethanol at 88oC, find
the final temperature of the system
when -500J of heat are lost.
(specific heat of water is 4.18
J/goC)
HINT:
Endothermic
reactions usually
________bonds
Exothermic reactions
___________bonds
PAGE 10… pick 5 processes you think are
endo and 5 that you think are exo
Combining atoms
producing sugar by
to make a
photosynthesis
molecule
evaporation
of water
cooking
separating
an egg
making ice
ion pairs
cubes
condensation of rain
splitting a gas
from water vapor
molecule apart
melting ice
cubes
formation of snow
a candle
in clouds
flame
Final page… pick 5 processes you
think are endo and 5 that you
think are exo
making ice cubes
formation of snow in clouds
melting ice cubes
conversion of frost to water vapor
condensation of rain from water vapor
evaporation of water
a candle flame
mixing sodium sulfite and bleach
forming a cation from an atom in the gas
phase
baking bread
rusting iron
burning sugar
cooking an egg
producing sugar by photosynthesis
forming ion pairs
Combining atoms to make a molecule in
the gas phase
mixing water and strong acids
separating ion pairs
splitting a gas molecule apart
mixing water with an anhydrous salt
making an anhydrous salt from a hydrate
crystallizing liquid salts (as in sodium
acetate in chemical handwarmers)
melting solid salts
mixing water and ammonium nitrate