Transcript Chapter 16
Energy – the ability to do work or produce
heat
◦ Kinetic energy – energy of motion
◦ Potential energy – stored energy
Chemical potential energy – stored energy because of
composition
Heat – energy process of flowing from a
warmer object to a cooler object
◦ Calorie – the amount of heat required to raise the
temperature one degree Celsius
◦ Joule – SI unit of heat and energy
When your body breaks down sugars and fats
to form carbon dioxide and water, these
exothermic reactions generate heat that can
be measured in Calories
Specific heat – amount of heat required to
raise the temperature of one gram of that
substance by one degree Celsius
Units - J/g ⁰ C
Large specific heats = Large amount of
energy to change temperature (water)
Small specific heats = Small amounts of
energy to change temperature (gold)
q = m x c x ∆T
q = mc∆T
q (heat)
c (specific heat)
m (mass of sample)
∆T (change in temperature)
The temperature of a sample of iron with a mass of 10.0g
changed from 50.4⁰C to 25.0 ⁰ C with the release of 114J heat.
What is the specific heat of iron?
q = mc∆T
Heat (q)
◦ 114J
Mass (m)
◦ 10.0g
Specific Heat (c)
◦ X
Change in temperature (∆T)
◦ 50.4⁰C - 25.0 ⁰ C = 25.4 ⁰ C
114 = 10.0(x)25.4
114 = 254(x)
X=.44881
Final answer 0.449J/g ⁰ C (3 significant figures and units)
Calorimeter – insulated device used for
measuring the amount of heat absorbed or
released during a chemical or physical
process
Thermochemistry is the study of heat
changes that accompany chemical reactions
and phase changes
Enthalpy (H) is the heat content of a system at
constant pressure
Enthalpy of reaction
◦ ∆Hrxn=Hproducts – Hreactants
Endothermic = absorbs heat giving the ∆Hrxn a positive number
Exothermic = releases heat giving the ∆Hrxn a negative number