Thermal Energy Flashcards
What is the Internal Energy of a Body
The sum of the randomly distributed kinetic energy and potential energy of the particles in a body
What do you Increase the Internal Energy of a System
- Do work on the system to transfer energy to it, (e.g moving its particles/changing its shape)
- Increase the temperature of the system
Why when the state of a substance is changed it’s internal energy also changes
Because the potential energy of the system changes, while the kinetic energy of the system is kept constant
Describe a graph showing how the internal energy of a substance varies with temperature
Describe the specific heat capacity equation
Q = mcθ
Energy required to change temperature = Mass x Specific Heat Capacity x Change in Temperature
What is Specific Heat Capacity
The amount of energy required to increase the temperature of 1 kg of a substance by 1 °C/1 K, without changing its state
What is the Specific Latent Heat Equation
Q = ml
Energy required to change the state of a substance = Mass x Specific Latent Heat
What is Specific Latent Heat
The amount of energy required to change the state of 1 kg of a substance, without changing its temperature
What are the Two Types of Specific Latent Heat
- Specific latent heat of fusion (when solid changes to liquid)
- Specific latent heat of vaporisation (when liquid changes to gas)
How would someone take a more accurate measurement of temperature
- Stir the liquid continuously before reading the temperature
- Take the temperature at different places to get an average
- Wait for the temperature to stablise before taking the measurement
How do you approach a Continuous Flow question
- Find the energy required to change the state of the first substance
- Find the energy required to change the state of the second substance
- Let the final temperature be T and sub this in
- Set up the equations as a pair of simultaneous equations
- The energy transfer is the same in both as the system is closed, we can equate these values to find the final temperature
What are the Three Gas Laws
- Boyle’s Law - when temperature is constant, pressure and volume are inversely proportional
- Charles’ Law - when pressure is constant, volume is directly proportional to absolute temperature
- The Pressure Law - when volume is constant, pressure is directly proportional to absolute temperature
Describe the Gas Law Graphs
What does Empirical mean
The gas laws are empirical in nature, meaning they are not based on theory but come from observation and experimental evidence
What is the Absolute Scale of Temperature
The absolute scale of temperature is the kelvin scale
How do you convert between Kelvin and Celsius
K = C + 273
What is the Absolute Zero Temperature
- -237°C or 0 K
- This is the lowest possible temperature
- It is the temperature at which particles have no kinetic energy and the volume and pressure of a gas are zero
Describe how the motion of the particles in an ideal gas changes as the gas approaches aboslute zero and describe how the motion of a real gas would change
- In an ideal gas, the particles cannot move so they reach absolute zero so they lose all of their kinetic energy
- For actual molecules some binding energy would still exist so they would freeze but some energy would still remain in form of bonds between atoms so there will be a level of vibration this means they can never reach absolute zero
What are the Ideal Gas Law Equations
- pV = nRT
Pressure x Volume = Number of Moles x Molar Gas Constant x Temperature
- pV = NkT
Pressure x Volume = Number of Molecules x Boltzmann Constant x Temperature
What is the value of the Molar Gas Constant
8.31 J mol-1 K-1
What is the Avogadro Constant
The Avogadro Constant is 1 mole of a substance which is equal to atoms/molecules 6.02 x 1023
What is the Boltzman Constant
- Molar Gas Constant / Avogadro Constant
- 1.38 x 10-23
What is the Equation for the number of moles in a substance
n = N/NA
Number of Moles = Number of Molecules / Avogadro Constant
What is the Molar Mass
Molar mass is the mass in grams of one mole of a substance
What is the Relative Molecular Mass
Approximately equal to the sum of the nucleons in a molecule of the substance
What is the Work Done Equation in Thermal Physics
Work Done = p x ΔV
Work Done = Pressure x Change in Volume
What assumptions are made for an Ideal Gas
- No intermolecular forces act on the molecules
- Molecules have negligible volume
- The motion of molecules in random
- Collisions are elastic
- The gas cannot be liquified
- The molecules move in straight lines between collisions
- The gas obeys all the gas laws at all temperures and pressures
What is Brownian Motion
- Brownian motion is the random motion of larger particles in a fluid caused by collisions with surrounding particles
- This can be observed through looking at smoke particles under a microscop
- Brownian motion contributed to the evidence for the existence of atoms and molecules.
Explain the gas laws using the simple molecular model
- Boyle’s law - Pressure is inversely proportional to volume at constant temperature (If you increase the volume of a fixed mass of gas, its molecules will move further apart so collisions will be less frequent therefore pressure decreases)
- Charles’s law - Volume is directly proportional to temperature at constant pressure (When the temperature of a gas is increased, its molecules gain kinetic energy meaning they will move more quickly and because pressure is kept constant, the frequency of collisions is constant so the molecules move further apart and volume is increased
- Pressure Law - Pressure is directly proportional to temperature at constant volume (When the temperature of a gas is increased, its molecules gain kinetic energy meaning they will move more quickly, as volume is constant the frequency of collisions between molecules and their container increases and they collide at higher speeds therefore pressure is increased)
Is the kinetic theory model emperical or based on theory
Based on theory
Why is an ideal gas’s internal energy the same as the kinetic energy of the gases atoms
- An ideal gas follows the gas laws perfectly, meaning that there is no other interaction other than perfectly elastic collisions between the gas molecules,
- This shows that no intermolecular forces act between molecules
- As potential energy is associated with intermolecular forces, an ideal gas has no potential energy
- Therefore its internal energy is equal to the sum of the kinetic energies of all of its particles
What is the equation for the kinetic energy of a gas molecule
1/2 m x (crms)2 = 3/2 x k x T = 3/2 x R x T / NA
1/2 x Mass x Root Mean Sqaure Speed = 3/2 x Boltzmann Constant x Temperature = 3/2 x Molar Gas Constant x Temperature / Avogadro Constant
Describe how the knowledge and understanding of the gas laws have changed over time
- The gas laws were discovered by a number of scientists and later explained by the development of the kinetic theory model
- However this model wasn’t accepted at first
- The understanding changed in accordance to the experimental evidence gathered by the scientific community
