Thermochemistry Flashcards
What is energy?
Ability to do work or transfer heat
What does work do?
Energy used to cause an object that has mass to move.
What does heat do?
Energy used to cause the temperature of an object to rise.
What is a system?
the molecules we want to study (thing you want to study
What are the surroundings?
are everything else
What is the first law of thermodynamics?
the total energy of the universe is a constant; if the system loses energy, it must be gained by the surroundings, and vice versa.
What is an open system?
can exchange both matter and energy with an outside system.
What is a closed system?
exchange energy but not matter with outside system
What is an isolated system?
Can exchange neither energy or matter with outside
What is the second law of thermodynamics?
- energy can be transferred as heat
- Heat flows from warmer objects to cooler until thermal equilibrium
What is Q?
the amount of energy required to raise the temperature of a substance by 1 Celsius
What is c?
the amount of energy required to raise the temperature of 1 g of a substance by 1 K.
What is internal energy (E)?
the sum of all kinetic and potential energies of all components of the system
What is enthalpy?
total heat content of a system
What is endothermic?
heat being absorbed
What is exothermic?
Heat being released
Why do some energy not let temperature rise?
Some of the energy is used to change in states
When water turns into steam, why is it at the same temperature for a long time?
Because the bonds are being broken
What is Hess’s Law?
“If a reaction is carried out in a series of steps, ΔH for the overall reaction will be equal to the SUM of
the enthalpy changes for the individual steps.”
What is bond dissociation?
energy needed to break one mole of the bond to give separated atoms - everything being in the gas state
How to measure reaction rate?
Anything over time (depletion of reactant or formation of products)
How to measure concentration?
- Change in volume
- remove small samples of a reaction mixture and perform titration
- use of a spectrophotometer
- Measure remaining mass
What increases rates of reaction?
- as concentration of reactants increase
- as temp increased
- with a catalyst -> lower activation energy
- as reactant surface area increases
What is the average rate?
Reaction rate over time
What is the average rate?
Reaction rate over time
What is instantaneous rate?
Reaction rate at any given time
What makes an effective collision?
- correct geometry
- sufficient energy (being absorbed or released)
What is activation energy?
Minimum amount of kinetic energy the reactants must have in order to react.
What affects the reaction rate?
- Nature of Reactants
- Concentration
- Temperature
- Catalyst
- Surface Area (Particle Size)
- Mixing (Stirring)
How does the nature of reactants affect rate?
Some reactants are more reactive than others
How does concentration affect rate?
Higher concentration = more collisions
How does temperature affect rate?
Higher temperature means faster collisions
How does catalyst effect rate?
Lowers the activation energy
How does particle size affect the rate?
Smaller the particle size = faster the rate
What is rate law?
how changes in the amount of a substance affect the rate of a chemical reaction
What does rate law tell us?
- shows the relationship between the reaction rate and the concentrations of reactants
- k is a constant that has a specific value for each reaction.
- The value of k is determined experimentally
- Exponents tell the order of the reaction with respect to each reactant.
What are elementary steps?
A reaction intermediate (or, reactants) is converted into the next reaction intermediate (or, products)
What is a reaction’s molecularity defined by?
the number of particles that participate as reactants in an elementary step.
Rate law vs overall rate law
Rate law: for all the steps (1 each)
Overall rate law is for the whole overall reaction
- Gives the R.D.S
What is the reaction mechanism?
sequence of actual events that take place as reactant molecules are converted into products
