Thermochemistry Flashcards
potential energy
energy stored due to an objects position relative to other objects, electric charge or internal stresses
chemical energy
energy that can be released through a chemical reaction
kinetic energy
energy associated with movement
thermal energy
energy associated with movement of particles that is responsible for its temperature
covalent bonds
bonds formed due to a shared pair of electrons
surroundings
everything around the reaction such as the reaction flask and the room (what we can typically measure)
reaction system
a mixture of reactants and products undergoing a reaction
open system
system that can exchange both energy and matter with its surroundings
closed system
system that can exchange energy but not matter with its surroundings
isolated system
system that cannot exchange energy or matter with its surroundings
temperature
a measure of thermal energy
state function
a property whose value does not depend on the path taken to reach that specific value, examples: number of atoms in a molecule in solid, liquid or gas state
heat
the amount of energy that is transferred from one system to its surroundings because of a temperature difference
work
the energy needed to move against a force.
enthalpy
the measurement of energy in a thermodynamic system
enthalpy change
the amount of heat energy transferred during a chemical reaction at constant pressure.
first law of thermodynamics
energy cannot be created or destroyed; it can only be converted from one form to another
endothermic reaction
a chemical reaction that absorbs heat due to products storing more energy than the products. This causes the temperature of the immediate surroundings to lower. Enthalpy is positive.
exothermic reaction
a chemical reaction that releases heat due to reactants storing more energy than the products. This causes the temperature of the immediate surroundings to rise. Enthalpy is negative.
bond dissociation energy
the amount of energy needed to break apart one mole of covalently bonded gases into a pair of radicals
energy profile
a theoretical representation of a chemical reaction or process as a single energetic pathway as the reactants are transformed into products.
activation energy
the amount of free energy that must be added to go from the energy level of the reactants to the energy level of the transition state.
standard enthalpy change
the enthalpy change that occurs when 1 mole of the substance is formed from its constituent elements in their standard states
specific heat capacity
the amount of heat that must be added to one gram of the substance in order to raise its temperature by 1 degree K
equation for heat of reaction
heat = mass * specific heat capacity * change in temperature
q = m * c * delta T
change in enthalpy
heat of reaction divided by moles
delta H = q/moles
Bond enthalpy
the enthalpy change when one mole of covalent bonds (in a gas) is broken under standard conditions. Bond breaking is endothermic and delta H is positive, bond building is exothermic and delta H is negative
homolytic fission
a covalent bond breaks and one electron goes back to each atom
heterolytic fission
a covalent bond breaks and both electrons in the bond go to one atom
Hess’s law
the enthalpy change accompanying a chemical reaction is independent of the pathway between the initial and final states
standard enthalpy change of combustion
the enthalpy change when one mole of a substance is completely burnt in oxygen under standard conditions. (found by reactants-products!)
hydrocarbon
a compound containing carbon and hydrogen only, named by mono-, di-, tri … and end in -ane, -ene or -yne
standard heat of formation
the enthalpy change when one mole of a substance is formed from its elements in their standard states under standard conditions. Value is zero for elements in their standard state.
ionization energy
the minimum amount of energy required to remove an electron from a gaseous atom. X(g) → X⁻ (g) + e⁻
enthalpy of atomization
the enthalpy change when one mole of a gaseous atoms is formed from an element in its standard state X2(g) → 2X(g)
electron affinity
the amount of energy released when an electron attaches to a neutral atom or molecule in the gaseous state to form an anion. X(g) + e⁻ → X⁻ + energy
Lattice enthalpy
the enthalpy change when one mole of ionic compound is broken apart into gaseous ions. AX(g) → A⁻ (g) + X+(g)
Oxidation
loss of electrons
Reduction
gain of electrons
Redox reaction
one atom loses electrons, while the other gains electrons
incomplete combustion
the burning of a substance in a limited supply of oxygen - when the substance is a hydrocarbon either carbon or carbon monoxide will be a product.
greenhouse gas
consist of carbon dioxide, methane, ozone, nitrous oxide, chlorofluorocarbons, and water vapor. Absorb infrared radiation and trap heat in the atmosphere
greenhouse effect
gases in a planet’s atmosphere insulate the planet from losing heat to space, raising its surface temperature.
biofuel
liquid fuels derived from renewable sources like plants and algae
biological carbon fixation
the process by which organisms convert inorganic carbon into organic compounds (ie, photosynthesis)
fermentation
a biological process where organisms convert carbohydrates, such as sugars or starch, into acids or alcohols which can be used as fuels
climate change
the change in earths climate due to man made factors such as the increase in atmospheric greenhouse gases like CO2, due to burning of fossil fuels
primary voltaic cells
a cell that produces electricity through an irreversible chemical reaction, but cannot be recharged
secondary voltaic cell
a rechargeable battery that can be recharged with electricity and reused many times
fuel cell
a type of electrochemical cell that uses the reaction between fuel and an oxidizing agent to produce electrical energy directly. It uses a continuous supply of reactants from an external source.
hydrogen fuel cell
A fuel cell uses the chemical energy of hydrogen for proton exchange to produce electrical energy
direct methanol fuel cell
a fuel cell that converts the chemical energy of methanol into electricity (cheaper and more readily available than hydrogen fuel)
spontaneous
a reaction that favors the formation of products at the conditions under which the reaction is occurring
nonspontaneous
a reaction that favors the reactants at the conditions under which the reaction is occurring
Equilibrium
a reversible chemical reaction in which no net change in the amounts of reactants and products occur
entropy
a measure of the disorder of a system
second law of thermodynamics
heat always flows spontaneously from hotter to colder regions of matter
standard entropy change
the change in entropy change under standard conditions. If delta S is positive entropy has increased.
standard entropy
the entropy of a substance at 100 kPa and 298K. Units are J K-1 mol -1
reaction quotient
the ratio of the concentrations of the reactants and the products at any point in time.
equilibrium constant
the ratio of the concentrations of the reactants and the products at equilibrium
