unit 2 vocabulary Flashcards
what is specific heat capacity
quantity of thermal energy required to raise the temperature of 1g of a substance by 1 degree celsius
- measured in J/g(celsius)
Why do your feet burn on the sand but cool off in water if the sun shines on both
because sand has a lower heat capacity compared to water (sand gets hotter faster than water does)
what is molar heat capacity
amount of heat energy to raise temperature of one mole of a substance by one degree celsius
what assumptions must be made for calorimeter
- any thermal energy transferred from the calorimeter to the outside environment is negligible
- any thermal energy absorbed by the calorimeter itself is negligible
- all dilute, aqueous solutions have the same density and specific heat capacity as water
q +
q -
+ : endothermic
- : exothermic
what is the relationship between surroundings and the system
- since matter can’t be created nor destroyed, the total thermal energy of the system and its surroundings remain constant
qsystem+qsurroundings=0
what is enthalpy
- refers to the total value of energy when its at constant pressure
- its symbolized by the letter H
- When a system reacts at a constant pressure it’ll either gain/lose energy, thus the enthalpy of the system has gone through a change
relationship between enthalpy and q
Hsystem= absolute value of qsystem
as long as pressure is constant
q= energy transfer due to thermal interactions
enthalpy= total energy of thermodynamic system (INCLUDING INTERNAL AND PRESSURE VOLUME ENERGY)
what does total enthalpy depend on
total kinetic energy + total potential energy, these values can never be determined which is why we measure change in enthalpy
If enthalpy is greater than reactants
absorption: endothermic
if enthalpy is less than reactants
release: exothermic
what does energy on the product sign show / negative sign
energy is released (exothermic)
what does energy on the reactant sign show / positive sign
energy is absorbed (endothermic)
potential energy diagram during endothermic vs exothermic reactions
exothermic: high to low (reactants greater than products)
endothermic: low to high (reactants less than products)
bond energies
bond energy- amount of energy absorbed or released when a bond is broken/formed
break bond: energy required
form bond: energy released
what is bond enthalpy
the enthalpy associated with breaking one mole of a particular bond in a gaseous substance
what is the quantity of energy required to break a chemical bond
dissociation energy
why is bond enthalpy always positive
energy is required to break chemical bonds
- energy is always released when a bond forms between gaseous fragments
greater bond enthalpy
stronger bond
bond energy per mole sign
always positive (bond energy per mole of bonds)
what is thermochemistry
the study of the energy changes that accompany physical or chemical changes in matter
what is energy
the ability to do work
what is work
the amount of energy transferred by a force over a distance
potential energy
the energy of a body or system due to its position or composition
kinetic energy
the energy of an object due to its motion
thermal energy
the total quantity of kinetic and potential energy in a substance
heat
the transfer of thermal energy from a warm object to a cooler object
temperature
a measure of the average kinetic energy of entities in a substance
open system
- a system in which both matter and energy are free to enter and leave the system
closed system vs open system vs isolated system
closed: a system in which energy can enter and leave the system, but matter cannot
isolated: an ideal system in which neither matter nor energy can move in or out
open: both matter and energy are free to enter and leave the system
what kind of system is a calorimeter
A calorimeter is an example of a closed system
heat vs temperature
heat:
- thermal energy in motion
- described energy that is flowing from one substances to another due to a diff in temperature
temperature:
- the measure of the average kinetic energy of the entities in a substance
- increasing temperature means the average kinetic energy of the molecules has been increased
chemical reactions and energy
- chemical reactions ALWAYS result in breaking of bonds between atoms and the formation of new bonds
- BREAKING BONDS CONSUMES ENERGY
- MAKING BONDS RELEASES ENERGY
- by comparing the energy consumed by bond breakage to the energy released from bonding making, a determination cam be made whether the net result is a storing of energy or release of energy
dissociation of NaOH
- when crystals of NaOH are dropped into water, the polar H2O molecules are attracted to the the ions in the crystal, which pull apart and forms a solution
chemical reactions in which energy is released
exothermic (bonds are being formed, surroundings feel hotter)
endothermic (h2o evaporating: adding energy to break H+ bonds
ex. sweat:
- true to inter and intra molecule
= IMF breaks (pulling energy out of surroundings causing surroundings to be cooler)
when energy is broken and it exceeds the energy of a bond, the net result is a decrease in temperature of a solution…
- where energy is being stored in the hydrated ions of the main molecule X
are Chem trails forming or breaking bonds?
formed bonds, condensing
what will happen to temperature in exothermic reactions
it will increase
- temp changes in h2o in calorimeter
- closed system (negligible: some energy will be lost)
system
surroundings
final-initial, reaction
initial-final, h2o
increased energy
- increased bond
(takes more energy to break it) - no IMF because they release energy when formed and broken
what does the hump on the graph represent
activation energy
what does the diff between reactants and products on the graph represent
change in enthalpy
which reactions are endothermic?
exothermic?
endothermic: melting, fusion, vapourization, sublimination
exothermic: dissolving, freezing, condensation, and deposition
How do you calculate enthalpy change
= (sum of moles of products(enthalpies of products)) - (sum of moles of reactants(enthalpies of reactants))
what is the rate of a reaction
change in concentration/change in time
negative slope
rate of consumption of reactants decreases
positive slope
rate of products produced increased
gradient of tangent to any point on the curve
rate of reaction at any instant
steeper the gradient
faster the reaction
at start of reaction, graph is the steepest
rate at the start of any reaction is always the fastest
as reaction progresses, gradient is becoming gentler
reaction is slowing down
after sometime, the graph levels off
point of levelling off signifies the end of the reaction
chemical nature of the reactants
- the more reactive the substance is, the faster the rate of the reaction
- unreactive metals like gold oxidize very slowly
- other metals like alkali’s oxidize very quickly
concentration of reactants
the rate of many chemical reactions increases at higher concentration of reactants
surface area
the greater the surface area, the more collisions of particles takes place and the faster the reaction
temperature
an increase in temperature increases kinetic energy of the particles, this in turn, increases the number of collisions and therefore the rate of the reaction
catalyst
- substance that alters the rate of a chemical reaction without itself being permanently changed
- provide an alternative energy pathway for the reaction, this lowers activation energy allowing more molecules to overcome the activation energy and produce products at a faster rate
- a catalytic converter increases the rate at which exhaust gases react with oxygen so that more of the exhaust products will be oxidized into harmless or less harmless substances
Collision theory
- chemical reactions can only occur if reactants collide with proper orientation and with enough kinetic energy to break reactant bonds and form product bonds
(an ineffective collision of oxygen and hydrogen molecules produces no reaction; the reactants bounce back unchanged)
(an effective collision of hydrogen and oxygen molecules produces water molecules)
sufficient energy + correct orientation in collision theory
sufficient energy:
- minimum amount of energy a reactant must have for a collision to be effective is called the activation energy
- overcomes the electrostatic repulsive forces between colliding entities
- weakening the bond of the
correct orientation:
- direct contact is requires for a equation to occur
there may be many collisions but only those that are in the proper reaction will cause a reaction to fell safe.
activation energy
minimum energy that colliding particles have to react, barrier for reactants to pass
describing reaction rates
when 2 reactant particles collide, they form as an activated complex which is an unstable form of electrons that forms a peak of the activation energy barrier and is short lived
what do catalysts do
speed up the reaction by lowering activation energy
enthalpy (catalyst graph slide)
enthalpy rises as reaction starts, energy is being put in to break bonds
Maxwell-boltzmann distribution
the area under the curve Ea, corresponds to the number of molecules with sufficient energy to overcome this barrier and rest
- if a catalyst is added, the activation energy is lowered, Ea will move to the left
- greater area under the curve, showing molecules have sufficient energy to overcome barrier in excess due to lowering of activation energy
-due to the many collisions taking place in gases , there is a spread of molecular energy and velocity
relative rates of reactions in order
electron transfer
collisions btwn 2 reactants
collisions btw multiple reactants
bond rearrangements
heterogeneous reactions (interface site)
