quiz 1 Flashcards
What is energy
Capacity to do work or produce heat
What are the two types of energy
Potential: due to position or composition
Kinetic: due to motion of an object (KE=1/2 mv^2)
What makes up internal energy
E = PE + KE
What does nature prefer
A lower energy state
Describe thermochemistry
Deals with heat effects accompanying chemical reactions
Always a flow of heat into or out of the system
Describe thermodynamics
Study of energy and its conversion into different forms
What is a system
Part of universe we focus our attention on
What is the surrounding
Everything else in the universe
What is temperature
Describes the random motion of particles in a substance
Higher temperature = greater motion
KEavg = 3/2 RT for an ideal gas
What is heat
Transfer of thermal energy between two objects due to a temperature difference (q or Q)
Flow from area of higher temperature to lower
Collisions push to object at lower temperature
What is work
A force acting over a distance, usually in joules, some energy is converted to heat because of friction
In chemistry, work = pressure volume work, expansion and compression of gases
State the first law of thermodynamics
Law of conservation of energy = energy can be converted from one form to another but can neither be created or destroyed
State the law of conservation of matter
Mass is neither created or destroyed in a chemical reaction
What is the equation for the energy of a system
ΔE = q + w
What is an exothermic reaction
Release heat energy to the surroundings
What is an endothermic reaction
Absorb heat energy from the surroundings
Describe the signs of ΔE, q and W for different types of reactions
Exothermic = ΔE < 0 & q = -
Endothermic = ΔE > 0 & q = +
Work done by system (expanding/losing energy) =
w = -
Work done on system (compressed/gaining energy) =
w = +
Whats the equation for work
w = -pΔv
What is the ideal gas law equation
pv = nRT pΔv = ΔnRT
What is a state function
Property that depends on the current state of function (E, p, v) and is independent of the path taken to reach current state
What is a path function
Work and heat depend on a specific pathway
What is enthalpy
A defined state function as the sum of all internal energy of a system and the product of its pressure and volume (under constant pressure)
State the equation for enthalpy
H = E + pv ΔH = E + pΔv ΔH = Qp
When does ΔH ≈ ΔE
At constant pressure
State Avogadros law
Volume of ideal gas is directly proportional to the number of moles of gas
What is an extensive property
Depends on the amount of substance (energy & enthalpy)
What is an intensive property
Does not depend on amount of substance (temperature)
What is a heat capacity
Amount of heat required to raise the temperature of the substance by one degree
What is q equal to
q = Cs x m x Δt q = Cn x n x Δt
What is thermal equilibrium
In a system where no energy is exchanged with surroundings q1 + q2 + q3 + … + qn = 0
What is calorimetry
Science of measuring heat (heat of reactions being determined experimentally)
What is the equation for coffee-cup calorimetry
ΔH = Qp (constant pressure )
What is the equation for bomb calorimetry
ΔE = Qv (constant volume)
What enthalpy occurs at a melting point
Enthalpy of fusion
Qfus = nΔHfus
What enthalpy occurs at a boiling point
Enthalpy of vaporization
Qvap = nΔHvap
What type of reactions are melting and boiling
Endothermic
Qphasechange = nΔHphasechange
What type of reactions are freezing and condensation
Exothermic
Qphasechange = -nΔHphasechange
What is hess’s law
Change in enthalpy is the same whether the reaction takes place in one step or series of steps
Describe the characteristics of hess’s law
Enthalpies can be added
Reaction reversed = sign of ΔH is flipped
Reaction is multiplied = multiply ΔH by the same
What is standard enthalpy of formation
The change in enthalpy associated with the formation of one mole of a compound from its elements with all substances in their standard states
ΔH*f
What are the standard states
Compounds = gases = 1 atm condensed states = pure liquid or solid solutions = concentration of 1 M Elements = 1 atm and 25*C ΔH*f of elements in their standard state = 0 **DIATOMIC STATES
What is the equation for standard Enthalpy of formation
ΔHrxn = Σ nΔHf (products) - Σ nΔH*f (reactants)
State the relationship of bond energy in an exothermic reaction
Potential energy of the products is lower than potential energy of reactants
State the relationship of bond energy in an endothermic reaction
Potential energy of the products is higher than potential energy of the reactants
What do bond energies represent
The amount of energy required to break 1 mole of bond (always positive)
What is the relationship between a bond length and its strength
Inverse relationship (stronger bonds = more pull so less length)
Describe stronger bonds
Lower in potential energy (more stable) than weaker bonds
What is the formula for bond strength calculations
ΔH = Σ n x D (bonds broken = reactants) - ΔH = Σ n x D (bonds formed = products)
