CHM135H1 Study Guide - Joule, Sodium Chloride, Calorie
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Chapter 6
Exam Preparation:
Concepts/Skills – Check List
Chapter 6
- First Law of Thermodynamics
The first law of thermodynamics (law of conservation of energy) states that the
total energy in the universe is conserved.
universe = system + surroundings = 0
- Definition of a State Function
State function: the internal energy of a system, dependent on the current state
(composition, volume, pressure and temperature) and not the path taken to reach
the state.
- Definition of System and Surroundings
System: part of the universe that we are focusing on
Surrounding: everything in the universe not including the system
- Sign convention from the System view
Energy Transferred as Heat Only
1. Heat flowing out of the system: q = negative and = negative
2. Heat flowing into the system: q = positive and = positive
Energy Transferred as Work Only
1. Work done by the system: q = negative and = negative
2. Work done on the system: q = positive and = positive
q
+
w
+
+
+
+
-
Depends on size of q
and w
-
+
Depends on size of q
and w
-
-
-
- Use of Hess’ Law of Heat Summation
Hess’ Law: the enthalpy change of an overall process is the sum of the enthalpy
changes in the individual steps
overall = 1 + 2 + 3 + …
- Be able to calculate heat released given number of moles, mass, or be
able convert heat to number of moles generated (all permutations)
Sample Problem 6.3
Finding the Quantity of Heat from a Temperature Change
Problem A layer of copper welded to the bottom of a skillet weighs 125 g. How
much heat is needed to raise the temperature of the copper layer from 25°C to
300.°C? The specific heat capacity (c) of Cu is given in Table 6.2.
Plan We know the mass (125 g) and c (0.387 J/g·K) of Cu and can find ΔT in °C,
which equals ΔT in K. We then use Equation 6.7 to calculate the heat.