Download Thermochemistry: Energy Relationships in

Thermochemistry: Energy Relationships in Chemistry
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Thermodynamics – the study of energy and its transformations.
Thermochemical changes – energy changes associated with chemical reactions.
System  that specific part of the universe of interest to us.
Surroundings  the part of the universe not contained in the system.
Three Types of Systems
• open system  exchanges mass and E
• closed system  exchanges E but no mass
• isolated system  no exchange of either mass or E
Different Types of Energy
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Energy – the ability to do work.
Thermal E – associated with the random motion of atoms and molecules.
Heat E – transfer of thermal energy between two objects at different temperature.
Chemical E – energy stored within the structural units of chemical substance.
Potential E – the ability of an object to do work because of its position in a field of
force.
• Kinetic E – the work that can be performed by a moving object rotational,
translational and vibrational
• The unit of energy : 1 Joule (J) =1 kg m2/s2
The Law of Conservation of Energy
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Energy is neither created nor destroyed in ordinary chemical and physical processes
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Chemical reactions either absorb or release energy.
Converted from one type into another.
First Law of Thermodynamics
Exothermic reaction  heat released to the surroundings.
Endothermic reaction heat supplied to the system by the surroundings.
Measuring energy changes
The experimental technique used for determining E changes is called calorimetry.
The amount of E lost or gained by a system is determined by three factors:
• the mass
• the temperature change
• the specific heat capacity
Specific heat capacity is the quantity of heat required to raise 1g of a sample 1 degree
Celsius
Calculating quantities of heat
q = m c T
q is the quantity of heat
m is the mass in grams
c is the specific heat capacity J/(goC)
Pg 799
T is the temperature change
Calculations Example 1
What would be the energy required if 50.0 g of iron is heated from 25.0 oC to 60.0 oC?
Calculations Example 2
What would be the final temperature if 1.00 kJ of heat were added to 100.0 g of water
at 20.0 oC ?