Thermal Properties of Matter (09) Flashcards
What is Internal Energy of a substance?
Internal Energy is the sum of Kinetic Energy and Potential Energy of a substance
It is the energy store that is made up of total kinetic energy associated with the random motion of particles and total potential energy between particles in a system
What is Kinetic Energy affected by?
Temperature
Increase in temperature causes particles to vibrate more vigorously, increasing the kinetic energy
Decrease in temperature causes particles to vibrate less vigorously, decreasing the kinetic energy
What is Potential Energy affected by?
Change in State
During change of state at constant temperature, only PE changes while KE remains the same
What is Heat Capacity?
Heat capacity is the change of its internal energy per unit change in its temperature
Formula of Heat Capacity?
Heat Capacity = Change in Internal Energy / Change in Temperature
What does Heat Capacity depend on?
Number of Particles. When there are more particles, more energy can be stored. Thus, objects with larger mass tend to have larger heat capacities.
Nature and strength of forces between particles. When forces between particles are stronger, more energy is needed to be transferred to the substance for each particle to gain a certain amount of kinetic energy. Thus, for the same volume, solids and liquids tend to have larger heat capacities than gases.
What is Specific Heat Capacity?
The change in internal energy per unit mass for each unit change in temperature
Formula of Specific Heat Capacity?
Specific Heat Capacity = Change in Internal Energy / Mass (Change in Temp)
How to determine a solid’s Specific Heat Capacity?
- Insulate a block of metal of known mass, m using lagging
- Insert a heater into a hole drilled into the metal block
- Insert a thermometer into a second hole drilled into the metal block to measure the temperature rise
- Record time, t using a stopwatch
Energy transferred electrically to metal = Gain in Internal Energy by metal
c = IVt / m (Change in Temp)
How to determine a liquid’s Specific Heat Capacity?
- Insulate a calorimeter of known mass, m and specific heat capacity, c
- Measure the mass of liquid using an electronic balance
- Insert heater into the liquid and heat directly
- Insert thermometer into the liquid to measure temperature rise
- Record time, t using a stopwatch
Energy transferred electrically by circuit = Internal Energy gained by Liquid and Calorimeter
c = IVt - mc (Change in Temp) / m (Change in Temp)
What is Melting?
Melting is the change in solid state to the liquid state when energy is transferred to the substance without change in temperature
What happens during Melting?
The molecules or particles of a solid are held together by strong intermolecular forces of attraction. For the solid to melt, the intermolecular forces must be weakened.
Once forces are weakened, particles can move out of their fixed positions. During that time, there will be no change in temperature and the energy transferred to the substance is known as the latent heat of fusion of a substance.
What is Latent Heat of Fusion?
It is the amount of energy transferred to change a substance between the solid and liquid states, while temperature is constant
What is Specific Latent Heat of Fusion?
It is the amount of energy transferred per unit mass of a substance to change between the solid and liquid states at constant temperature
Specific LHOF = LHOF / Mass
What is Boiling?
Boiling is the change in solid state to the liquid state when energy is transferred to the substance without change in temperature
What happens during Boiling?
Energy is supplied to overcome the intermolecular forces of attraction between particles or molecules in a liquid. They move far apart and forces of attraction between particles are negligible. The energy is also used to push back on atmospheric pressure as substance expands.
When liquid is boiling at constant temperature, the energy absorbed is known as the latent heat of vaporisation.
What is Latent Heat of Vaporisation?
The amount of energy transferred to change between liquid and gaseous states while temperature is constant
What is Specific Latent Heat of Vaporisation?
The amount of energy transferred per unit mass to change between the liquid and gaseous states while temperature is constant
What are the differences between Boiling and Evaporation?
Boiling:
1. Occurs at a particular temperature
2. Occurs throughout the liquid
3. Temperature remains constant throughout process
4. Quick Process
5. Produces bubbles during process
6. Requires external source of energy
Evaporation:
1. Occurs at any temperature
2. Occurs only at surface of the liquid
3. Temperature may change during process
4. Slow Process
5. No bubbles produced during process
6. Energy is supplied by the surrounding medium
How does Evaporation occur?
Molecules that are the near the surface of liquid and have high KE are able to escape into the air, leaving the less energetic particles behind. Average KE of the liquid become lower, causing decrease in temperature. Energy from surrounding air is transferred to the liquid and KE of molecules increase again. Step 1 is repeated.
Factors affecting Evaporation?
- Temperature
The higher the temperature, the higher the rate of evaporation. Particles which are higher in temperature have higher KE, which allows them to escape easier. - Exposed Surface Area
The greater the ESA, the higher the rate of evaporation. More particles are able to escape at the same time. - Humidity of Surrounding Air
The higher the humidity, the lower the rate of evaporation. When it is less humid, there is a larger concentration gradient of gas molecules above surface of liquid and surrounding air. Diffusion of gas molecules occur more readily. - Motion of Air
The greater the motion of air, the higher the rate of evaporation. When there is more motion of air, gas molecules are constantly being carried away from surface of liquid, maintaining a steep concentration gradient for gas molecules to diffuse. - Atmospheric Pressure
The lower the atmospheric pressure of air, the higher the rate of evaporation. Gas molecules have less chance of colliding with air particles back into the liquid. - Boiling Point of Liquid
The lower the boiling point of the liquid, the higher the rate of evaporation. The intermolecular forces of attraction of particles in the liquid are lower.
