Chapter 2: 2.1 Heat, Work, and Energy Flashcards
Define:
Thermodynamics
The study of the energy changes involved in physical and chemical processes
Define:
Thermochemistry
The branch of thermodynamics that investigates the heat flow that occurs during these reactions
Explain the difference between a “food/large calorie” (Cal) and a “small calorie” (cal)
Food calories are typically seen on food packages, and are actually 1000 cal
Small calories are used in thermodynamics
Define:
1 calorie
1 small calorie is equal to 4.184 Joules
Define
1 Calorie
1 Cal = 4.184 kJ
What is another well known definition of a large/food calorie?
Approximately the amount of energy needed to raise the temperature of 1 kg of water by 1 degrees Celsius (4.184 kJ)
True or False:
Heat always flows from cool to warm
False, heat always flows from the warmer object to the cooler object
State:
3 types of systems
- Open system
- Closed system
- Isolated system
Define:
Open system
Can exchange both matter and energy with its surroundings
Define:
Closed system
Can exchange energy but not matter with its surroundings
Define:
Isolated system
Exchanges neither matter nor energy with its surroundings
Define:
Energy
“The capacity to do work”
Work is defined as the product of a force acting on an object and the distance that the object moves in response to the force
What type of work are chemists usually interested in?
Pressure-Volume (PV) Work
Define:
Pressure-Volume Work
Work involved in the expansion or compression of gases
State and formula and units of:
PV work
w = -P * ΔV
Units in kPa L (1 kPa L = 1 J)
List and describe:
Some types of energy
- Heat energy (thermal energy): The energy transferred due to a temperature difference bewteen the system and the surroundings
- Kinetic energy: The energy associated with motion
- Potential energy: Stored energy or the energy a body possesses due to its position
True or False:
Chemical energy is a form of thermal energy
False, chemical energy is a form of potential energy
True or False:
Energy can be created
False, energy cannot be created/destroyed; it can only be converted
Define:
Heat capacity
The parameter used to estimate the heat energy associated with temperature changes
What is a related quantity to heat capacity?
Specific heat capacity
What is the amount of heat transferred denoted by? What is it related to?
- Denoted by q
- Related to temperature difference (ΔT) and heat capacity/specific heat capacity
For heat capacity, state:
- What it is used for
- Notation
- Units
- Usually used for objects
- Represented by the symbol C
- Units: Joules/Degrees Celsius
State the relation/formula for:
Heat capacity
(State the variables)
q = C * ΔT
* q: Amount of heat energy
* C: Object’s heat capacity
* ΔT: Temperature change
For specific heat capacity, state:
- Definition
- Notation
- Units
- The heat needed to warm one mass unit (g or kg) of a substance by one degree
- Represented by lowercase c
- SI unit: Joules/Kilogram * Degrees Celsius
- Common unit: Joules/Gram * Degrees Celsius
State the relation/formula for:
Specific heat capacity
q = m * c * ΔT
True or False:
When calculating amount of heat transferred, all Celsius units can be swapped with Kelvin units
True, as we are using the temperature difference
Define:
Temperature change
The difference between final and initial temperatures
* ΔT = Tfinal - Tinitial
When calculating temperature difference:
What do we have to ensure?
Tfinal and Tinitial are using the SAME SCALE
When a system absorbs energy from the surroundings…
The process is endothermic and change in energy is positive
When a system releases energy to the surroundings…
The process is exothermic and the change in energy is negative
State the relation between:
ΔT and energy change (q)
- -ΔT = -q, system cools
- +ΔT = +q, system warms
True or False:
The sign of q is the same as sign of ΔT
True
Does heat move from cool to warm or the other way?
Heat always goes from warm to cool
In heat transfer between objects:
State the change of heat, ΔT, and q for the warmer object
- Loses heat and cools down
- ΔT < 0
- q (lost) is negative
In heat transfer between objects:
State the change of heat, ΔT, and q for the cooler object
- Gains heat and warms up
- ΔT > 0
- q (gained) is positive
What must the number of joules lost by the warmer object equal to?
The number of joules gained by the cooler object
What is it called when both objects reach the same final temperature (Tf)? What is a formula that represents this?
Thermal Equilibrium
* -q (lost) = q (gained)
Define and give examples of:
Intensive (intrinsic) property
A property that has the same value regardless of the sample size
* E.x. Temperature (melting and boiling points), Density
Define and give examples of:
Extensive (extrinsic) property
A physical property whose value increases with the sample size
* E.x. Mass, Volume, Energy, Enthalpy, and Entropy
Define and give examples of:
State function
A property whose value depends ony on the current state of the system, not on how that state was reached
* E.x. Volume, Pressure, Enthalpy
* NOT Heat and Work
State:
1st Law of Thermodynamics
The total energy of an isolated system is conserved
How do we keep track of the energy of a system?
A thermodynamic function called * Internal Energy (E)*
Define:
Internal energy (E)
E is the sum of all the kinetic and potential energies of all the atoms, ions, and molecules in the system
Can internal energy be measured?
No it cannot, but change in internal energy can be measured
What are some ways to measure ΔE?
q - heat
w - work
For a system at constant pressure, how is work calculated?
w = -P * ΔV
In gas expansion, state:
- How is work being done
- Value of w
- Change in work energy
- Gas (system) does work on surroundings
- w is negative
- Lost work energy
In gas compression, state:
- How is work being done
- Value of w
- Change in work energy
- Surroudnings does work on gas (system)
- w is positive
- Gained work energy
What happens if the process does not involve a compression or expansion? What would be the value of w?
- The change in volume would be zero
- The value of w is zero
What does ΔE equal?
ΔE = q + w
Determine what happens to the internal energy of the system when:
Surroundings do work on, or supply heat to the system
- Internal energy of the system increases
- ΔE > 0
Determine what happens to the internal energy of the system when:
The system does work on, or supplies heat to the surroundings
- Internal energy of the system decreases
- ΔE < 0
When the system is kept at a constant volume, what happens to the relationship with ΔE?
- w = 0
- The relationship becomes E = q, commonly written as E = qv
The subscript v in qv signifies the constant volume
Theorem:
What does the internal energy changes of a system equal when the volume doesn’t change?
The internal energy change of a system is equal to the heat transferred when the volume does not change
