Thermochemistry - Nature of Energy Flashcards
What is thermochemistry?
The study of energy changes during physical or chemical changes in matter
What do all thermodynamics depend on?
The law of conservation of energy
The law of conservation of energy states…
Energy cannot be created nor destroyed
Potential Energy (PE)
- Energy due to the position or composition of an object
- Stored Energy
Kinetic Energy (KE)
- Energy of motion
- Depends on mass of object and its velocity
Calculation of thermal energy
Thermal Energy=PE + KE
Changes that occur in matter may be classified into….
Physical, chemical or nuclear changes
Physical Change
- Change in form or state of a substance
- No chemical bonds are broken
- Least energy
Chemical Change
- Change in chemical bonds between atoms resulting in new substances
Nuclear Change
- Change in the protons or neutrons in an atom resulting in a new atom
- Most energy
What is a System?
The substance undergoing a change
What are the surroundings?
- Describes the system’s environment
- Includes all matter that is not part of the system
What is thermal energy?
- Total amount of movement (kinetic energy) of the particles in a system and the stored energy within these particles (potential energy)
What does thermal energy depend on?
- How many particles are moving and their temperature
What is temperature?
- Measures the average speed of particles in a sample
- Measured in ℃ or K
What is heat?
- The amount of thermal energy transferred between substances
- Due to a temperature difference
- Measured in Joules (J)
Extensive Property
- Directly depends upon the amount of substance
Example of an extensive property
Heat
Intensive Property
- Not related to the amount of the substance
Example of an intensive property
Temperature
State Function
Property that depends only on its current state and not on how that state was reached
Exothermic - Thermal energy (q)
Released
Exothermic - Direction of the flow of heat
System —> Surroundings
Exothermic - Temperature Change
- Tf>Ti
- ΔT>0
- Postive
Exothermic - Sign of ΔH
- ΔH<0
- Negative
Exothermic - Energy Term
- Product
- A + B —> C + energy
Endothermic - Thermal Energy (q)
Absorbed
Endothermic - Direction of the flow of heat
Surroundings —> System
Endothermic - Temperature Change
- Tf<Ti
- ΔT<0
- Negative
Endothermic - Sign of ΔH
- ΔH>0
- Postive
Endothermic - Energy Term
- Reactant
- A + Energy —> B + C
Open System
- Both matter and energy can move between the system and the surroundings
Open System Example
Boiling pot of water
Closed System
Can exchange energy but not matter with its surroundings
Closed System Example
Covered pot of water
Isolated System
- Neither energy nor matter can move into or out of the system
- Will still be some energy loss
Isolated System Example
Insulated thermos
