Chemistry Journal
7.02 Enthalpy Values
Driving Questions: How do scientists calculate enthalpy for physical and chemical changes,
and how does that help distinguish between endothermic and exothermic changes?
Key Ideas and Terms
Notes
FQ: How is specific heat capacity related to temperature?
What is specific heat
capacity?
the quantity of heat required to raise the temperature of one
gram of a substance by one degree Celsius
Why is specific heat
capacity an intensive
property?
It is an intensive property because the amount of the substance
does not change its specific heat capacity.
How does a change in
mass affect how much
thermal energy is
needed to change the
temperature of a
substance?
However, a difference in mass does impact how much thermal energy
must be absorbed before a change in temperature occurs. For instance,
when the same amount of heat is applied, an ocean will take a lot
longer to change temperature than a small lake.
Video: Specific Heat Capacity

What units of
measurement are
used to measure
specific heat
capacity?
It is measured in joules per gram degrees Celsius. It can also be
measured in joules per gram Kelvin.

What is the formula
for specific heat
capacity?
It can be calculated using the following formula—specific heat, or C,
equals heat generated by the temperature change, or Q, divided by the
mass of substance times the change in temperature.
Does low specific heat
equal lower melting
point? Explain why or
why not.
Yes
FQ: How are energy transfers calculated using a temperature change?
How do chemists
calculate energy
transfers in an
The energy transfer of an unknown sample can be calculated using the
specific heat capacity of the sample, the temperature change observed
during the reaction, and the mass of the sample.
unknown sample?
Video: Calculating Enthalpy

What is the
equation to
calculate enthalpy?

Show how to use
the enthalpy
equation from the
video example.
q equals m times c times delta T
Describe each variable
of the enthalpy
equation.
How is change of
temperature
determined for the
enthalpy equation?
A flask containing 855
grams of water was
heated over a Bunsen
burner. If the
temperature of the
water was raised from
21.0 to 85.0 degrees
Celsius, how much
heat (in joules) did the
water absorb? Describe
the steps.
The specific heat
capacity of liquid water
is 4.184 J/g ⁰ C.
When using the specific heat capacity equation to calculate enthalpy,
the change in temperature (△T) can be determined by subtracting the
initial temperature of a substance from the final temperature.
Use the common specific heat capacities table to help you solve the practice problems below. Be
sure to include a copy of the table to your chemistry journal.
A frying pan with 5
grams of vegetable oil
is heated on a stove
top. If the temperature
of the oil increases
from 25.0 °C to 95.0
°C, how much energy
does the oil absorb?
Calculate the number
of joules released when
72.5 grams of water at
95.0 °C cools to a final
temperature of 28.0 °C.
How does enthalpy
change during phase
changes?
FQ: How is the heat of reaction calculated for a chemical reaction?
What is the heat of
reaction?
the change in the enthalpy of a chemical reaction that occurs at a
constant pressure
What is the equation to
calculate the heat of
reaction?
What is the total
enthalpy change of a
reaction?
The total enthalpy change in a reaction is a combination of the energy
used to break bonds in the reactants and the energy released when
bonds are formed in the products.
How does △H become
positive or negative?

Endothermic

Exothermic
How can enthalpy
change be used as a
conversion factor to
determine heat of
reaction?
The enthalpy change of a reaction or process is usually expressed in
kilojoules per mole (kJ/mol) in a thermochemical equation.
What is a
a balanced chemical equation that shows the enthalpy change in a
thermochemical
reaction?
reaction
The chemical reaction
and enthalpy change
for burning methane
(CH4) is given below.
If 38.5 grams of
methane are burned,
how many kilojoules of
energy are transferred,
and is this reaction
endothermic or
exothermic?
CH4 + O2 → CO2 +
2H2O
△H = −890.0 kJ/mol
During an endothermic
reaction, H for the
reactants was −200
kJ/mol. What range of
values could the H for
the products be for this
reaction?
The combustion of
isooctane fuel (C8H18)
has an enthalpy change
of −5,460 kJ/mol. How
many kilojoules of
energy are released
when 350.0 grams of
isooctane are burned?
Be sure to record any extra helpful notes, vocabulary terms, and practice sample problems.