ch 11: thermodynamics

Definition

• Thermo: Temperature
  
  

• Dynamics: Change or movement
  
  

What is Temperature?

• A measure of the average kinetic energy of particles in an object.
  
  

• Hot: Particles move faster as temperature increases.
  
  

• Cold: Particles move slower as temperature decreases.
  
  

Laws of Thermodynamics

1. First Law:
   
   

   • Energy cannot be created nor destroyed, only transformed.
     
     

2. Second Law:
   
   

   • Energy flows from hot to cold.
     
     

   • Objects of different temperatures exchange energy until reaching equilibrium.
     
     

Methods of Heat Transfer

1. Conduction:
   
   

   • Heat transfer through physical contact between objects of different temperatures.
     
     

   • Example: A hot plate.
     
     

2. Convection:
   
   

   • Heat transfer through movement of fluids (liquids and gases).
     
     

   • Example (liquid): Boiling water.
     
     

   • Example (gas): Oven.
     
     

3. Radiation:
   
   

   • Heat transfer through electromagnetic waves.
     
     

   • Example: Sunlight.
     
     

Temperature Changes and Heat Energy

• Energy changes affect elements and compounds differently.
  
  

• Temperature change depends on:
  
  

  1. Mass of the element/compound.
     
     

  2. Specific heat of the element/compound.
     
     

Specific Heat

• Definition: The amount of energy needed to raise 1 gram of a substance by 1°C.
  
  

Comparison:

• Sand: Lowest specific heat (requires less energy to heat).
  
  

• Water: Highest specific heat (requires more energy to heat).
  
  

Specific Heat Depends On:

1. Type of molecule.
   
   

2. Molecular arrangement.
   
   

3. Molecular interaction.
   
   

Solving Specific Heat Problems

• Use the specific heat formula:
  
  q = mc\Delta T
  
  Where:
  
  

  • q: Heat energy (Joules)
    
    

  • m: Mass (grams)
    
    

  • c: Specific heat (J/g°C)
    
    

  • \Delta T: Temperature change (°C)

Calculating Temperatures

Formula for Heat Energy

Q = m \cdot C_p \cdot \Delta T

Where:

• Q: Heat energy (Joules)
  
  

• m: Mass (grams)
  
  

• C_p: Specific heat capacity (J/g°C)
  
  

• \Delta T: Change in temperature (°C)
  
  

Steps to Calculate \Delta T:

1. Determine the final temperature (T_f).
   
   

2. Determine the initial temperature (T_i).
   
   

3. Calculate \Delta T:
   
   \Delta T = T_f - T_i
   
   

Interpreting Q:

• Positive Q: Heat energy is absorbed.
  

• Negative Q: Heat energy is released.