Chapter 5 Flashcards
What is energy?
ability to do work or transfer heat
What is work?
energy used to cause an object that has mass to move over some distance
What is heat?
energy used to cause the temperature of an object to rise
What is thermodynamics?
the study of energy transformations
What is thermochemistry?
applies thermodynamics to chemcial reactions
What is kinetic energy?
energy an object has due to its motion
What is the equation of kinetic energy (KE)?
KE = 1/2 mv^2
What is potential energy?
energy an object has due to its position in space or chemcial composition (bonds it has)
What is electrostatic potential energy?
the potential energy in molecules | E(el)
What is the equation for electrostatic potential energy?
E(el) = (k Q1 Q2) / d
What is “k” in the electrostatic potential energy equation?
proportionality constant = 8.99 * 10^9 Jm/C^2
How many joules is 1 calorie?
4.18 J
What is the First Law of Thermodynamics?
energy is neither created nor destroyed as it can be converted into different forms
What is a “system”
the parts/stuff we want to study
What is “surroundings”?
everything else that surrounds the system
What is the equation for work?
w = Force x distance
What are 3 types of systems?
open | closed | isolated
What is an open system?
matter and energy can be exchanged with their surroundings
What is a closed system?
ONLY energy can be exchanged with surroundings NOT matter
What is an isolated system?
NEITHER energy and matter can be exchanged with surroundings
What is internal energy?
E | sum of ALL kinetic and potential energies of all components of the system
What are the 3 parts of thermodynamic quantities?
number | unit | sign (+) or (-)
What does a (+)delta E mean?
Ef > Ei | endergonic energy change
What is an endergonic energy change?
system GAINED / ABSORBED energy from surroundings
What does a (-)delta E mean?
Ef < Ei | exergonic energy change
What is an exergonic energy change?
system LOST / RELEASED energy into surroundings
What is the equation for the change in internal energy (delta E)?
q (heat) + w (work)
What does a +q mean?
system GAINS heat (increase temperature)
What does a -q mean?
system LOST heat (decreased temperature)
What does a +w mean?
work is done ON the system
What does a -w mean?
work is done BY the system
What is endothermic?
heat ABSORBED by the system
What is exothermic?
heat RELEASED by the system
What is a state function?
property of a system that is determined by specifiying the system’s condition/state in terms of temperature, pressure, etc.
What does the value of the state function depend on?
ONLY the present state of the system INDEPENDENT from the path it took to get there
How is internal energy (E) a state function?
depends ONLY on the initial and final states of the system | q and w are not state functions
What is enthalpy?
heat flow
What is the equation for enthalpy?
E + PV
What is pressure-volume work (PV)?
work involved in the expansion or compression of gases
What does deltaH = q(p) mean?
the change in enthalpy equals the heat (q) gained or lost at constant pressure
What does a (-)deltaH mean?
exothermic
What does a (+)deltaH mean?
endothermic
What is the equation for deltaH for chemcial reactions?
Hproducts - Hreactants
What is enthalpy of reaction?
enthalpy change that accompanies a reaction | deltaHrxn = heat of reaction
What are thermochemical equations?
balanced chemical equations that show the associated enthalpy change
What are the 3 “truths” about enthalpy?
its an extensive property | (+)deltaH in forward direction and (-)deltaH in reverse direction | deltaH for reactions depends on the state of products and reactants
What does it mean that enthalpy is an extensive property?
magnitude of deltaH is proportional to the amount of reactant consumed in the process
What is calorimetry?
the measurement of heat flow
What is a calorimeter?
device used to measure heat flow
What is heat capacity?
amount of energy required to raise the temperature of a substance by 1 K (1 degC) for 1 mol substance
What is specific heat capacity?
amount of energy required to raised the temperature of 1g of substance by 1 K (1 degC)
What is the equation for specific heat capacity (Cs)?
heat transferred (q) / (mass x temperature change)
What must first be done when carrying out a reaction in aqueous solution in a constant-pressure calorimetry?
calculate the heat change for the water in the solution first
In a constant-pressure calorimetry, what does exothermic indicate?
reaction lost heat which water gains (water is surroundings)
In a constant-pressure calorimetry, what does exothermic indicate?
reaction gains heat which water lost
What is q(soln)?
the heat gained or lost by the solution
What is q(rxn)?
the heat gained or lost by the reaction
What is the relationship between q(rxn) and q(soln)?
opposites of each other | q(soln) = -q(rxn)
What is the Cs (specific heat capacity) of water?
4.184 J/gk
What is the equation for heat(q)?
m Cs (deltaT) “mcAT”
What is a bomb calorimeter?
constant-volume calorimetry that carries out combustion reactions
What is a “bomb”?
small cup with insulated sealed vessel carrying out combustion reactions | designed to withstand high pressures
What is a combustion reaction?
compound reacts completely with excess O2
What is the heat equation for a bomb calorimetry?
q(rxn) = - C (deltaT)
What does Hess’s Law state?
because H is a state function = deltaH for the overall reaction SHOULD EQUAL the sum of all enthalpy changes of each reaction from each step | H1 = H2 + H3
What are enthalpies of formation (deltaHf)
enthalpy change for the reaction in which a compound is made from its constituent elements in their elemental forms
What is the standard enthalpy of formation (deltaHof)?
enthalpy change of a compound for a reaction forming 1 mol compound
What is bond enthalpy?
the enthalpy change for breaking a bond in 1mol of a gas
