Energy Flashcards
Thermodynamics
- The study of energy transfer that we can measure in the macroscopic words
- Does not make any assumptions about the microscopic world (like KMT)
- Heat transfers until thermal equilibrium is established
- ΔT measures energy transfer
Energy
- The capacity to do work or produce heat
- Most energy can be exchanged between objects through contact
Work
Form of energy based on moving an object over a distance
Heat
- The form of energy that flows betweem 2 objects because of their difference in temperature
- Quantity of hotness (mass + speed)
- Thermal energy
Temperature
Average kinetic energy
What is a calorie
- heat required to raise ttemp of 1.00 g of H2O by 1.0 °C
Units of energy
- cal –> kcal
- kcal –> Cal
- cal –> joules
- 1000 cal = 1 kcal
- 1 kcal = 1 Calorie (a food “calorie”)
- 1 cal = 4.184 joules
First law of thermodynamics
The total energy content of the univerws is constant
Potential energy
Stored energy that an object has by virtue of its position or compsotion
Kinetic energy
energy of motion or energy of a reaction
5 forms of energy (PE or KE)
- Electrical - KE
- Heat / thermal energy - KE
- Light / radiant energy - KE
- Nuclear - PE
- Chemical - PE
Internal energy
- sum of all forms of KE (motion of atoms/molecules) and PE (rep by tthe chemical bonds and IMFs) in a system
- E = internal energy
- E = PE + KE
System
The object under study
Surroundings
Everything outside the system
Direcionality of heat transfer
- Heat always transfers from hoter objec to cooler one
Exothermic reaction
- heat transfers from system to surroundings
- PE of products < PE of reactants
Endothermic reaction
- heat transfers from surroundings to system
- PE of products > PE of reactants
Change in energy equation
- ΔE = q + w
- change in energy = heat + work
- if isolated system (closed) then ΔE of system = 0
q, w, ΔE signs (+ or -)
- +q: system gains energy
- -q: system releases heat
- +w: system gains energy from work (compression)
- -w: system releases energy by doing work (expansion)
- +ΔE: system gains energy
- -ΔE: system releases energy
work equation
- w = -PΔV
- constant pressure
Heat capacity (c)
- The heat required to raise an object’s temp by 1 C
- Cup vs tub: tub has higher heatt capacity
Specific heat
- The amount of heat required to raise the temp of one gram of a substance by one degree celsius
- H2O: 4.184 J / gºC
- How much energy is tranferred due to temp difference?
- The heat (q) lost or gained is related to
- sample mass
- change in T
- specific heat capacity
specific heat equation: q=
q = smΔT
Calorimetry
- The amount of heat absorbed or released during a physical or chemical change can be measured, usually by the change in temp of a known quantity of water in a calorimeter
Enthalpy
- A state function that accounts for heat flow in the processes (chemical or physical) that occurs at constant pressure when no forms of work are performed except P-V work
- No gas, no change in volume
- H = ΔE + PΔV
- ΔH = q (at constant P)
- For a chemical reaction:
- ΔH = Hproducts - Hreactants
State function
- A property that is independent of the pathway
- Enthalpy
- Temperature
- Energy
Not state functions
- Heat and work
Rate
change in property / time
3 things must happen to molecules in order for a reaction to occur
- Collide
- Energy to react (have to collide with enough force)
- Orientation
Activated complex
Top of hill on energy diagram
Rate determining step
Slowest reaction is the RDS
Exothermic fast vs slow reaction
- Fast: small upward hill
- Slow: large upward hill
