Chapter 5: Thermochemistry Flashcards
What does the term ‘pressure-Volume Work’ describe?
Work done by or to a system to exert or resist pressure in scenarios involving constant pressure
For the purposes of chapter 5, all reactions are considered to be under constant pressure in one way or another (because they either occur under constant pressure from the Earth’s atmosphere or inside of containers with lids)
What is the concept of enthalpy meant to describe/quantify?
The flow/measure of heat that occurs in a system during a reaction (like neutralization) or process (like phase change)
what does Hess Law state?
that the total enthalpy of a rxn it equal to the sum of the enthalpies of its intermediate rxns
what types of reactions are more accurately studied with constant PRESSURE calorimeters?
solutions
What is the equation for enthalpy?
H= E + PV where P is constant and E is the system’s total energy
What are the base units for Newtons?
N = kg(m/s^2)
What does ‘Internal Energy’ refer to?
The sum of a system’s total energy: heat plus work
where heat and work can both have positive or negative values, depending on the situation
What are the 3 state functions related by the concept of enthalpy (H)?
Pressure
Volume
Energy
What is the purpose of the concept of ‘Enthalpy’
‘Enthalpy’ allows us to relate the state functions pressure, volume, and energy in a way that lets us set DELTA enthalpy equal to q when a system is under constant pressure
What is the gist of the First law of thermodynamics?
that energy cannot be created or destroyed; it has to come from somewhere and go to somewhere
By extension: Heat/work gained by the system is lost by the surroundings (and vice versa)
why doesn’t the expression for the heat capacity of constant volume/bomb calorimeters include mass?
because Ccal is based the heat capacity of the entire machine, not by the heat capacity of individual grams or moles of the water it contains
Does Potential Energy pertain to motion, temperature, storage, or intermolecular attraction?
Stored energy (related to position) that can be converted to kinetic energy
Has types: gravitational potential energy (pertains to objects), chemical (pertains to energy stored in chemicals that can be used to do work), electrostatic (pertains to charged particles), and spring/elastic (pertains to energy stored in things that are stretched or compressed)
what does Calorimetry measure?
the heat transfer (delta enthalpy) between a system and its surroundings based on the magnitude of the temperature changes that occur
what does ThermoCHEMISTRY examine?
the Transformation of energy (especially heat) in chemical rnxs
Is enthalpy considered a state function?
yes, because it is composed of/relates 3 state functions: E, P, V
Is the water in a calorimeter a solution?
No. water is a compound.
Why/when is it that in thermo calculations, ‘work’ can cancel with -‘PdeltaV’?
In DELTA!!! enthalpy calculations, when pressure is constant, work = - work, and thus cancels in the equation
How many joules are in 1 Calorie?
1 calorie = 4.184J
Amount of energy needed to RAISE 1 gram of water by 1 degree
what types of reactions are more accurately studies with constant VOLUME calorimeters?
combustions
What are joules units for?
energy
What is the gist of the equation for delta enthalpy of reaction?
net heat = heat require to produce products - heat required to react reactants
In a calorimetry experiment involving solutions, what/whose heat capacity issued for heat calculations?
The water’s heat capacity is used (provided the solution is considered dilute)
what does Molar heat capacity describe/quantify?
the amount of Energy req to RAISE 1 mol of a material by 1 degree (celsius or kelvin)
What is the term ‘Energy’ meant to describe?
The ‘fuel’ needed to do work or transfer heat (where work is energy transfer involving motion and heat is energy transfer involving temperature change)
