Transcript Chapter 10
Energy
10.1 The Nature of Energy
Energy: the ability to do work or
produce heat
Potential energy (store energy):
energy due to position or
composition
Kinetic energy (motion energy):
energy due to motion of the object
and depends on the mass of the
object and its velocity
KE = ½ (mv2)
Law of conservation of energy:
that energy can be converted from
one from to another but can be
neither created or destroyed.
Energy of the universe is constant
The nature of energy
Work: force acting over a
distance
W = F/d
State function: property of
the system that changes
independently of its pathway
Which of the following are state
functions, and which are not
The temperature of an ice cube
The volume of an aerosol can
The amount of time required
for a 10 mi bike ride
10.2 Temperature and Heat
Temperature: is a measure of the random motions of the
components of a substance
E.g H2O molecules move rapidly in hot water than in cold
water
Heat: a flow of energy due to a temperature difference
Tfinal = average temp from mixing (hot & cold temp)
10.3 Exothermic and Endothermic
Process
System – everything
we focus on in
experiment
Surroundings –
everything other the
system
exothermic (energy
flows out of system to
surrounding (via heat)
endothermic ( energy
flows into system from
surrounding (via heat)
Examples
Identify whether these process are exothermic or
endothermic
Your hand gets cold when you touch ice
The ice melts when you touch it
Propane is burning in a propane torch
Two chemicals mixing in a beaker give off heat
10.4 Thermodynamics
Is the study of energy.
First law of thermodynamics: the energy of the universe is
constant
Internal energy – energy of the system
∆E = q x w
∆ => change in the function
q => represents heat
W => represents work
10.5 Measuring Energy changes
calorie: the amount of energy (heat) required to raise the
temperature of one gram of water by 1oC
1Calorie = 1000 calories
Joule (J) – SI unit
1 calories = 4.184 joules
Converting Calories to Joules
Express 60.1 cal of energy in units of joules
How many calories of energy corresponds to 28.4 J?
Specific heat
The amount of energy
required to change the
temperature of one gram
of a substance by 1oC
Denoted as s
Heat required = specific
heat x mass x change in
temp
q = s m ∆T
Calculating Energy Requirements
Determine the amount of energy (heat) in joules required to raise
the temperature of 7.40 g water from 29.0oC to 46.0oC
A 5.63 g sample of solid gold is heated from 21oC to 32oC. How
much energy in Joules and calories is required?
A sample of gold requires 3.1 J of energy to change its
temperature from 19oC to 27oC. What is the mass of this sample
of gold
A 55.0 g aluminum block initially at 27.5oC absorbs 725 J of
heat. What is the final temperature?
10.6 Enthalpy
Heat of reaction (∆H) = the amount of heat that being
absorbed or release by a given reaction
∆Hp = heat
Enthalpy
When 1 mol of methane (CH4) is burned at constant
pressure, 890 kJ of energy is released at heat. Calculate
∆H for a process in which a 5.8 g sample of methane
is burned at constant pressure
The reaction that occurs in the heat packs used to treat
sports injuries is
4Fe(s) + 3 O2(g) 2Fe2O3(s) ∆H= -1652 kJ
How much heat is released when 1.00 g of Fe(s) is
reacted with excess O2(g)
Entropy
Entropy (S) – measure of
disorder or randomness
Randomness increase -> S increases
Sgas> Sion >Smolecule>Ssolid
Ssolid = 0
E.gH2O(s) H2O (l)
H2O (l) H2O (g)
H2O (g) H2O (l)
S=+
S=+
S=-
2nd law of thermodynamic: the
entropy of the universe is always
increasing