2B4 Heat, Energy, and Thermochemistry Flashcards
Explain the core principles of thermodynamics, including state and path functions, heat transfer, temperature, and enthalpy.
Define:
state functions
Intrinsic properties of a system that depends only on the present state of the system, not on the path taken to reach it.
Examples: Pressure, temperature, internal energy, mass, volume, density, entropy, and Gibb’s free energy.
Define:
path functions
Properties that depend on the path taken to move from one state to another.
Path functions vary based on the process or method used to transition between states.
Examples include heat and work.
What are the key differences between state and path functions?
- State functions depend on the present state, while path functions depend on the path taken.
- State functions give consistent values, unlike path functions.
These distinctions are critical for thermodynamic calculations and concepts.
What is the difference between work and heat?
- Work: The energy required to move an object over a distance.
- Heat: The energy that raises the temperature of an object.
Both are ways energy is transferred, but they differ in their effects and processes.
What is the difference between thermodynamics and thermochemistry?
- Thermodynamics: The study of heat transformations.
- Thermochemistry: The study of heat changes in chemical reactions.
These fields are fundamental in understanding energy transfer in systems.
What is the difference between a system and its surroundings?
- System: The part of the universe chosen for study.
- Surroundings: Everything outside the chosen system.
The system and surroundings together make up the universe.
How can state and path functions be compared to moving between points A and B?
The position between A and B is a state function (constant), while time taken to move from point A to B depends on the path (e.g., walking, driving).
This analogy highlights the dependence of path functions on the route taken.
Define:
temperature
The measurement of the average kinetic energy of the particles in a substance.
It indicates how fast the particles are moving; hotter substances have faster-moving particles.
What mnemonic can help remember Celsius temperature ranges?
- 30 is hot
- 20 is nice
- 10 is cold
- zero is ice
This helps in recalling the relative temperatures on the Celsius scale.
What is the difference between heat and temperature?
- Temperature: A measure of random motion of particles.
- Heat: The transfer of energy due to temperature difference.
Understanding this distinction is important in thermodynamics.
Heat always moves from a hotter object to a cooler one until thermal equilibrium is achieved.
Define:
thermal energy
It is the total kinetic energy of all particles in a substance.
Unlike temperature, thermal energy depends on both mass and temperature.
How does thermal energy differ from temperature?
Thermal energy depends on the total energy of particles; temperature measures the average energy.
Large objects can have more thermal energy at the same temperature due to their greater mass.
Fill in the blanks:
Water freezes at ____°C and boils at ____°C.
0; 100
This is equivalent to 32 °F and 212 °F on the Fahrenheit scale.
List three scales used to measure temperature.
- Kelvin
- Celsius
- Fahrenheit
These scales are used in different scientific and regional contexts.
What is the difference between Kelvin and Celsius scales?
The celsius scale starts at 0 while the kelvin scale starts at 273.
The Kelvin scale is an absolute temperature scale, while Celsius is relative.
The two are related by the equation K = °C + 273
What temperature in Kelvin corresponds to 22 °Celsius?
295 K
This is calculated by adding 273 to the Celsius temperature.
How do you convert Fahrenheit to Celsius?
°C = (5/9)(F - 32)
This equation is rarely used in chemistry.
The Celsius scale is preferred for temperature measurement.
What is the lowest temperature possible on the Kelvin scale?
Absolute zero (0 K)
At absolute zero, there is theoretically no molecular movement; kinetic energy ceases.
It represents the lowest limit of the thermodynamic temperature scale.
State the symbol and unit for heat transfer.
Symbol: Q
Unit: Joules (J)
Q represents the energy transferred as heat during a process.
What is the formula for heat transfer?
Q = m × C × ΔT
where:
- Q: heat transfer
- m: mass
- C: specific heat capacity
- ΔT: temperature change
Define:
calorimetry
It is the science of measuring heat transfer in a system.
It involves devices called calorimeters.
List the two types of calorimeters.
- Coffee cup calorimeters
- Bomb calorimeters
Coffee cup calorimeters operate at constant pressure, while bomb calorimeters work at constant volume.
State the equation for calorimeter heat transfer.
Qhot = Qcold + Qcal
This accounts for heat transfer between hot and cold substances and the calorimeter itself.
How do calorimeters function?
They measure heat transfer by having a substance absorb heat from a test substance, with surrounding water indicating temperature change.
They operate on the concept that heat lost by the test substance equals heat gained by the water.
What parameters must be measured during calorimetry experiments?
- Mass of the water.
- Mass of the test substance.
- Initial temperatures.
- Final temperatures.
List three units used for measuring heat.
- British Thermal Units (BTU)
- Calories
- Joules
What is a BTU?
The amount of energy required to raise the temperature of 1 pound of water by 1 degree Fahrenheit.
It is roughtly equivalent to 1055 J.
This unit is commonly used in heating and cooling applications.
Define:
heat capacity
The quantity of heat energy required to raise the temperature of a substance by one unit.
It depends on the mass, temperature difference, and nature of the substance.
What is specific heat capacity?
The quantity of heat required to change the temperature of unit mass of a substance by one unit.
It includes the mass of the substance in the definition unlike the heat capacity.
How can you determine the specific heat capacity of an unknown substance?
By using calorimetry to compare experimental results to published results.
This involves measuring heat transfer in a calorimeter.
Fill in the blank:
The SI unit of specific heat capacity is _____ .
Joules per kilogram per Kelvin (J/kg·K).
This unit is derived from energy (J), mass (kg), and temperature (K).
State the formula for specific heat capacity.
C=Q /(mΔT)
C is the specific heat, Q is heat, m is mass, and ΔT is the temperature change.
Which substance has the highest specific heat capacity among common substances?
Water, with a specific heat capacity of 4186 J /kg.K.
A high value of heat capacity implies that a high amount of heat energy is required to change the temperature of a substance by a certain degree.
The high specific heat capacity of water makes it a good coolant.
Define:
molar specific heat capacity
The amount of heat required to raise the temperature of one mole of a substance by one unit.
Molar specific heat depends on the number of moles rather than mass.
