Thermodynamics(09-01-08->present)

Thermodynamics, which came from the Greek word "therme" meaning heat and "dynamis" meaning power, is a branch of physics and is used extensively in chemistry and biochemistry.It studies the effects of changes in temperature, pressure, and volume on physical systems at the microscopic scale by analysing the collective motion of their particles using statistics. Roughly, heat means "energy in transit" and dynamics relates to "movement"; thus, in essence thermodynamics studies the movement of energy and how energy instills movement. Historically, thermodynamics developed out of need to increase the efficiency of early steam engines.(http://en.wikipedia.org/wiki/Thermodynamics#The_laws_of_thermodynamics)



Thermodynamics has 3 Laws:



1. The first law states that the energy of the universe is constant. It can only be transformed from one form to another.(conservation of energy)

equation:

∆E = heat(q) + work(w)

where work = -P∆V and the -P is the opposing pressure

so the equation for this law is:

∆E = q - P∆V



2. The 2nd law states the ∆S (change in entropy) of the universe must always increase.(entropy)

to predict whether a reaction is spontaneous or not. There are things that we should follow:

• whenever the ∆G(Gibbs Free Energy) is negative, the reaction is spontaneous;


• the reaction is spontaneous at all times if ∆H and ∆G are both negative and only ∆S is positive;


• the reaction is spontaneous when the temperature is high and when ∆S and ∆H is positive;


• the reaction is spontaneous when the temperature is low and when ∆H, ∆S, ∆G is negative; and


• the reaction is nonspontaneous if only the ∆S is negative.

3. The 3rd law states that the entropy of a crystalline substance is zero at the absolute zero temperatue. (absolute zero temperature)

just add water.,september

the next activity is about the changes in thermal energy. first we will define thermal energy. thermal energy is heat energy in transfer. heat is a form of energy. when heat it is in the process of being transferred, it is called thermal energy.



the objective of this activity is to know what will happen if you add cold water to the hot water when both have the same mass.



materials:

• 4 plastic foam cup


• scissors


• balance


• thermometer


• hot and cold water

procedure:

• label the first cup with H for hot water and the second cup with C for cold water.


• get the 2 cups then cut 2 to 3 cm from the top of each cup. using a pencil, poke a hole on the bottom of each cup, make sure that the thermometer will fit on both cover. label both cup with C and H.


• measure the mass of cup without the cover. record.


• add hot water (1/3 of the cup) to the cup labeled H and cold water (same amount) to the cup labeled C.


• measure their mass then their temperature. record.


• pour the cold water to the hot water. measure the temperature. record.

conclusion:

if you add cold water to the hot water with the same mass, the temperature will change because the heat coming from the water is absorbed by the cup then as you add cold water in it, the absorbed heat is transferred again to the water. the amount of heat transferred is equal to the amount of heat absorbed by the cup.

Thermal Energy is the kind of energy that is related to and/or caused by heat. When thermal energy is applied to a substance, the average velocity of the particles or molecules which make up the substance increases -- and it gets warmer!

thermochemistry(08-23-08)

you know what thermochemistry means? thermochemistry is a branch of chemistry that deals with the relationship between chemical action and heat or the quantitative study and measurement of heat and enthalpy changes. thermochemistry, generally, is concerned with the heat exchange accompanying transformations, such as mixing, phase transitions, chemical reactions, etc., which includes calculations of such quantities as the heat capacity, heat of combustion, heat of formation, etc.
thermochemical equation shows the relationship energy changes and mass relationship.
example:
H2(g) + 1/2 O2(g) --> H2O(l); ∆H = -285.8 kJ (exothermic-heat is released)
HgO(s) --> Hg(l) + 1/2 O2(g); ∆H = +90.7 kJ (endothermic-heat is absorbed)

there are guidelines that are to be remembered in writing this equations:

• always specify the physical states of all reactants and products

example:

liquid H2O to solid H2O the ∆H is +6.01 kJ/mol

solid H2O to liquid H2O the ∆H is -6.01 kJ/mol

• when both sides of thermochemical equation is multiplied by a factor ,n, then ∆H must also change by the same factor

example:

2H2O -> 2H2O ∆H=2(6.01 kJ/mol)=12.02 kJ/mol

• when we reverse the equation, we change the role of products and reactants. as a consequence, the sign changes but the magnitude of ∆H for the equation remains the same

example:

liquid H2O to solid H2O the ∆H is +6.01 kJ/mol
solid H2O to liquid H2O the ∆H is -6.01 kJ/mol

solving for thermochemical equations:

problem:

Calculate the heat evolve when 74.6 g of SO2 is converted to SO3.

SO2(g) + 1/2 O2(g) -> SO3(g) ∆H = -99.1 kJ/mol

get the number of moles of SO2:

74.6g SO2x 1 mol of SO2 / 64.07g SO2 = 1.16 mol SO2

*64.07 g of SO2 is the molar mass of SO2 which is to be computed first if it is not given. to compute the molar mass, get the mass of S and 2O. after you get their mass, combine them by adding the mass of S and 2O.

multiply the answer to the ∆H which is -99.1 kJ/mol:

= (1.16 mol SO2)(-99.1 kJ/mol) ->cancel the mol

heat evolve = -115 kJ