AP chemistry Thermodynamics
Freezing point and melting point are at what temperature
0c
the standard enthalpy of a eleent or compund is measure at what temperature and pressure
1 atm and 25 degrees celcius
Example #5: A 25.6 g piece of metal was taken from a beaker of boiling water at 100.0 °C and placed directly into a calorimeter holding 100.0 mL of water at 25.0 °C. The calorimeter heat capacity is 1.23 J/K. Given that the final temperature at thermal equilibrium is 26.2 °C, determine the specific heat capacity of the metal.
1) We know this: qlost, metal = qgained 2) However, energy is gained by two different entities (the water and the calorimeter itself). Therefore: qlost, metal = qgained, water + qgained, calorimeter 3) Substituting, we have: (mass) (Δt) (Cp, metal) = (mass) (Δt) (Cp, water) + (Δt of water) (calorimeter constant) 4) Putting values into place and solving: (25.6 g) (73.8 °C) (x) = (100.0 g) (1.2 °C) (4.184 J/g °C) + (1.2 °C) (1.23 J/K) x = 0.266 J/g °C Comment #1: the °C and the K cancel in this case because (1) one °C is the same size as one K and (2) the 1.2 °C is a temperature difference, not a temperature of 1.2 °C.
the specific heat for water in joules
4.184 J/g C
how many jules in 1 calorie
4.2 Joules
What a State Function ?
A State Function is a thermodynamic quantity whose value depends only on the state at the moment, i. e., the temperature, pressure, volume, etc... The value of a state function is independent of the history of the system.
intensive Property
A physical or chemical property that does not change with the amount of matter. For ∆E, ∆H, ∆S, & ∆G to be intensive properties, the temperature, pressure, mass, and physical state of a substance must be precisely defined.
what the equation of the relationship between heat capacity and specific heat
C=ms m is mass of the substance in grams and example the spefic heat of water is 4.184 j/g *C and the heat capacity of 60.0g is 60.0g is * 4.184 j/g *C = 251 J/C
relationship of heat capacity and specific heat ( this is the book way)
C=ms C= heat capacity m= mass s= specific heat capacity
what do you need to calculate qcal
Ccal times delt t
Condensation and boiling for water is at what temperature
Condensation and boiling point is 100c for water
Extensive Property
Extensive Property A physical or chemical property that varies in proportion to the amount of matter. ∆E, ∆H, ∆S & ∆G are extensive properties.
what is the equation for enthalpy and what is the symbol for enthalpy and what do each thing/symbol repersents
H = U + PV H is the symbol for enthalpy and U is the symbol for the internal energy of the system and P and V are the pressure and volume of the system there all state functions
Heat Definition:
Heat Definition: Heat is the form of energy that flows between two samples of matter due to their difference in temperature. Usually denoted by the letter Q or q.
specific heat capacity units in means fo grams specific heat capacity in means of moles
J/grams* K J/mol*K please keep in mind and can be in celsius as well
breaking bonds making bonds do what
absorb energy releases energy
The first law of thermodynamics second third Zeroth law
also known as Law of Conservation of Energy, states that energy cannot be created or destroyed in an isolated system. The second law of thermodynamics states that the entropy of any isolated system always increases. of thermodynamics states that the entropy of a system approaches a constant value as the temperature approaches absolute zero. zeroth law of thermodynamics - If two thermodynamic systems are each in thermal equilibrium with a third, then they are in thermal equilibrium with each other.
The phases that have the most potential energy are( order)
are gas ,liquid ,solid
Heat always flows from warm to
cold
the equation for the standards enthalpy of a reaction
delta H°rxn = (the capital funny e looking shape)ndeltaH°f( this all represents the products) - (same funny e)delta H °f ( reactants) m and n represent the stoichiometric coefficients for the reactants and the products and the fuuny e or actual the greek letter sigma means means the sum of. to use the equation we must know the delta H °f values of the compunds that take part in the reaction. products goes first
rules for writing a thermochemical equation
do almost same for normal equation symbol of state etc.
melting and boiling are ....... freezing and condensation are ............
endothermic exothermic
Heat of Fusion endothermic Changes from Liquid to Solid state Heat of Vaporization Liquid to Gas Exothermic
endothermic Changes from Liquid to Solid state Liquid to Gas Exothermic
ok the words to know if it is exothermic or endothermic
endothermic : melting,boiling,sublimation(solid to gas),absorbed exothermic: freezing condensation,deposition(gas to solid) use these and the information given by the question to ermine if exo or endo no more of the just looking at the temperature and seeing if it endo or exo
laws of conservation of mass and laws of conservation of energy
energy not crated or destroyed all energy can be accounted for work
How to tell entropy in a chemical equation
entropy gas>liquid>solid and count compounds no individual atoms increase in how many compounds and phase then entropy is incressing
how is a reaction exothermic how is a reaction endothermic
exo: if the energy releases in the formation of hydrated ions delta H3 is greater than the amount of energy required to separate solute and solvent particles (H1 + H2) then the sum delta H will be negative and reaction will be exothermic end:if the amount of energy in the formation of hydrated ions is less than the amount of energy to separate solute and solvent then the energy change will be positive and reaction is endothermic
heat is a extensive prop so
extensive property, so the change in temperature resulting from heat transferred to a system depends on how many molecules are in the system.
equation : 2H2O(g) + O2(g)→ 2H2O(g) ΔH=-483.g kj/mol what is the Enthalpy change when 178g of h20 are produce
find the moles and multiply by H 178g/16/2 * times NEGATIVE 483 = -2390 kj for the most part from what we know divide by molar ratio do not multiply and divide
how to determine the correction factor qcal
for heat of solution calculations, the heat capacity of the calorimeter, also called the calorimeter constant, must be determined experimentally. The calorimeter constant has units J/oC. This calibration experiment is done by mixing equal volumes of hot and cool water in the calorimeter and measuring the temperature after 20 sec- onds. The resulting value is assumed to be the instantaneous mixing temperature, Tmix. The average temperature Tavg of the initial hot (TH) and cool water (TC) is also calculated: Tavg = (TH + TC)/2
what does C cal stand for
heat capacity of the calorimeter
what does qcal represent
heat changes of the calorimeter
constant - volume calorimetry
heat of combustion is usually measured by placing a know mass of a compound in a staial container and called a constant - volume bomb calorimeter which is filled with oxygen with about 30 atm per pressure the closed bomb is immersed in water. the sample is then
conduction
is a situation where the heat source and heat sink are connected by matter. As we discussed before, the heat flows from the source down the temperature gradient to the sink. It is different from convection because there is no movement of large amounts of matter, and the transfers are through collisions. The source and the sink are connected.
convection
is the way heat is transferred from one area to another when there is a "bulk movement of matter." It is the movement of huge amounts of material, taking the heat from one area and placing it in another. Warm air rises and cold air replaces it. The heat has moved. It is the transfer of heat by motion of objects. Convection occurs when an area of hot water rises to the top of a pot and gives off energy.
consent - pressure calorimetry
it determines the heat change of non-combustional things can be costed from two Styrofoam coffee cups this device measure the effects of variety of reaction such as acid base neutralization as well of heat of solution and heat of dilution. cause pressure is content qrxn is equal to the enthalpy change delta H we treat the calorimeter as a isolated system futhermore we negated the capacity of the coffee cup in our calculation
what are the units for the heat of reaction
kj
what the units for enthalpy
kj/mol
the indirect method
most compounds can not be directly synthesized this method is base on Hess law Heat of reaction problems When your finish it should be the same problem on top only do heat thing for compounds ( where you write equation out and have heat there to) when you have multiply of compound ex 3h20 you gotta multiply delta H by 3. When you have a compound to the left of the equation or the reactant side of the equation do it "reverse" basically write chemical with compound on same side (left) but on heat sheet they have reactant first so you write it reverse But if you write it reverse you have to change the delta H if negative write positive and vis versa Cross off if have the same thing on opposite side If have multiply of you can add If compound is on right side no change it. Look carefully at h20 l and g our different The delta heat is in kcal Also if compound doubled so is the reactants.
why might it be important to now the standard enthalpy of formation
once we know the values we can calculate the standard enthalpy of a reaction , (delta H° rxn) defined as the the enthalpy of a reaction carried out at one atm
466g sample of water is heated from8.50c to 74.60c calculate the amount heat absorbed in kilojoules by water
(466g) * (4.184j/g*c )(74.00c-8.50) divide by j 1000 129 KJ
Temperature is also an intensive property so that means
, which means that the temperature doesn't change no matter how much of a substance you have (as long as it is all at the same temperature!).
qsoln = -(q(aq) + q(cal)) what does this equation mean ?
When measuring the heat transfer for an exothermic heat of solution using a calorimeter, most of the heat released is absorbed by the aqueous solution (qaq). A small amount of the heat will be absorbed by the calorimeter itself (qcal). The overall heat transfer (qsoln) for the reaction (the system) then becomes:
radiating energy
When the transfer of energy happens by radiation, there is no conductive medium (such as in space). That lack of medium means there is no matter there for the heat to pass through. Radiation is the energy carried by electromagnetic waves (light). Those waves could be radio waves, infrared, visible light, UV, or Gamma rays. Heat radiation is usually found in the infrared sections of the EM spectrum.
in class for specific heat capacity of water and the q equation what is the way they do it in class
specific heat capacity of water is 4.184 j/g*°C and they use C for specific heat capacity
specific heat
specific heat of a substances is the heat require to rise the temperature of one gram of a substance by one degree Celsius it has the units J/g C it is an intensive property
Hess's Law of Constant Heat Summation (or just Hess's Law)
states that regardless of the multiple stages or steps of a reaction, the total enthalpy change for the reaction is the sum of all changes. This law is a manifestation that enthalpy is a state function.
if you have one beaker of boiling water that is 2 liters and another which is 1 liter the temperature is different or the same and what the temperature ?
temp same, both boiling temp is 100°C because temperature is define as average kinetic energy where as the 1 liter water has less heat then the 2 liter water
MOLAR heat capacity
the energy in joules required to raise the temperature of 1 mol of substance by 1c or 1k units : J mol⁻¹ K⁻¹ or J mol⁻¹°C⁻¹ equation Cm= C/n molar heat capacity equals = molar mass X specific heat \Cm=g/mol X J/g*°C
specific heat capacity (guards definition) equation for specific heat per gram (also got from guard)
the energy in joules required to rise the temperature of 1 gram of substance by 1 c or 1 k units: J g⁻¹ K⁻¹ or J g⁻° C⁻¹ Cs = C/M
heat capacity
the heat capacity of a substances is the amount heat required to raise the temperature of a given quality of a substance by one degree celsius J/C it is a extensive property
what is calorimetry
the measurement of heat change
heat
the transfer of thermal energy (causes temperature differences)
finding the delta H° f the direct method
this method work for compounds that can be readily synthesized from there element for example CO2 carbon(graphite) + O2 → CO₂g delta Hrxn = -393.5 kj/mol thus can be written delta H °rxn = delta H°f (CO2g) - [delta H°f(C graphite ) + delta H°f(O2,g)] = - 393.5 because graphite and O₂ are most stable we can assume both zero therefore deltaH °rxn =delta H°f (CO2,g)=-393.5 kj/mol delta H °f 9CO2,g)= -393.5 kj/mol assigning zero to most stable form of element in stander state does not effect calculation
state function
value depends only on state of system, not on how system arrived at that state
how to do heat of reaction problems your way or the way or way you learned in first year
when given an equation first balance it and if it is a compound on reactants side keep it/write it backward then the way on the sheet that way delta H will be negative and if compound is on product side delta H is the same as the sheet and write it the same way as sheet as if compound is multiply you have to multiply the entire equation by that coefficient NEW thing that not really thought in hills only the equation that need more is doubled and if standard quality how grater coefficient then you you divide the delta H and equation by that coefficient then add all delta Hs up and cross of things on opposite side of equation
what is Hess law ( the one in Change text book)
when reactents change into products , the change in enthalpy is the same whether the reaction take place in takes places in one step or in a steps
more stable allotrope for instance oxygen O2 is said to have standard delta H at (delta H °f ) .............
zero
if process occurs at constant pressure the enthalpy of a system = heat lost or gained by the system
ΔH = H finial - H initial = qp p is just a greek letter for constant pressure
Hess's Law
•Heats of reaction are additive when chemical reactions are added. •If the coefficients of a chemical reaction are multiplied by a constant, then ∆H⁰(r) is also multiplied by that same constant.
one KJ equals how many J
1000 J
one liter equal to
10⁻³ or m³
how many joules in kilojoules
1KJ equals 1000J
0 Celsius how many kelvin
273
Surprisingly exothermic :
Surprisingly exothermic : o2 and h2 to make h20 and rusting it just take longer why don't see heat/frie
When a 1.000 g sample of the rocket fuel hydrazine, N2H4, is burned in a bomb calorimeter which contains 1200 g of water, the temperature rises from 24.62°C to 28.16°C. If the C for the bomb is 840 J/°C, calculate reaction for combustion of a one-gram sample qreaction for combustion of one mole of hydrazine in the bomb calorimeter
or a bomb calorimeter, use this equation: qreaction = -(qwater + qbomb) qreaction = -(4.18 J / g·°C x mwater x Δt + C x Δt) qreaction = -(4.18 J / g·°C x mwater + C)Δt where q is heat flow, m is mass in grams, and Δt is the temperature change. Plugging in the values given in the problem: qreaction = -(4.18 J / g·°C x 1200 g + 840 J/°C)(3.54°C) qreaction = -20,700 J or -20.7 kJ it basically broken up in water plus bomb calorimeter part now know that 20.7 kJ of heat is evolved for every gram of hydrazine that is burned. Using the periodic table to get atomic weights, we can calculate that one mole of hydrazine, N2H4, weight 32.0 g. Therefore, for the combustion of one mole of hydrazine: qreaction = 32.0 x -20.7 kJ/g qreaction = -662 kJ
HEAT ! is represent BY
q
what does this mean ????? q = mCpDT
q = quantity of heat (joules or calories) m = mass in grams DT = Tf - Ti (final - initial) Cp = specific heat capacity (J/g ºC) Every pure substance involved in a chemical reaction has a unique heat capacity, and the heat capacity of 1 mol of a pure substance is known as its molar heat capacity (J/mol-K or J/mol-ºC). The heat capacity of 1 gram of a substance is known as its specific heat (J/g-K). The following equation relates the specific heat of a substance, the temperature change, the mass of the substance, and how much energy was put into the system:
Heat, is
q, is thermal energy transferred from a hotter system to a cooler system that are in contact
what the equation to calculate the enegry/heat release in
q= M * C * delta T specific heat capacity M mass of the substance and change in temp is delta T
what are the equation for calculating the heat change
q=m s delta t q = C delta t t is temperature change delta t = t final - t initial
remember qcal mean so q system = qcal + qrxn =0 qrxn =-qcal to calculate the heat of the calorimeter you will need heat capacity of calorimeter thus qcal =Ccal ΔT
qcal=acronym stands for heat in the calorimetry qrxn= acronym stands for heat reaction
The temperature of 110 g of water rises from 25.0°C to 26.2°C when 0.10 mol of H+ is reacted with 0.10 mol of OH-. Calculate ΔH for the reaction look at this carefully remember water and delta H will be different not necessary in the the value but in the sign Calculate ΔH if 1.00 mol OH- reacts with 1.00 mol H+
qwater = 4.18 (J / g·°C;) x 110 g x (26.6°C - 25.0°C) qwater = 550 J the water is positive because it is gaining that energy where as the ΔH of the REACTION IS negative because the temperature increase thus it is exothermic so ΔH = to H = -(qwater) = - 550 J We know that when 0.010 mol of H+ or OH- reacts, ΔH is - 550 J: 0.010 mol H+ ~ -550 J Therefore, for 1.00 mol of H+ (or OH-): ΔH = 1.00 mol H+ x (-550 J / 0.010 mol H+) ΔH = -5.5 x 104 J ΔH = -55 kJ
