[theunraveler]

these are the few which i dunno where to begin...some help will be much appreciated

1) the reaction below releases 56.6kj of heat at 298k for each mole of NO2 formed at a constant pressure of 1 atm. what is the standard enthalpy of formation of NO2 given the standard enthalpy of NO is 90.4kj mol

2NO + O2 ---> 2NO2

2) a 200g of copper at 100 degrees celsius is dropped into 1000g of water at 25 degrees celsius. what is the final temp of the system?

specific heat of water is 4.18J and copper is 0.400 J

3) if the equilibrium constant for A + B <===> C is 0.123, the equilibrium constant when 2C <===> 2A + 2B is?

[T_N_T]

these are the few which i dunno where to begin...some help will be much appreciated

1) the reaction below releases 56.6kj of heat at 298k for each mole of NO2 formed at a constant pressure of 1 atm. what is the standard enthalpy of formation of NO2 given the standard enthalpy of NO is 90.4kj mol

2NO + O2 ---> 2NO2

2) a 200g of copper at 100 degrees celsius is dropped into 1000g of water at 25 degrees celsius. what is the final temp of the system?

specific heat of water is 4.18J and copper is 0.400 J

3) if the equilibrium constant for A + B <===> C is 0.123, the equilibrium constant when 2C <===> 2A + 2B is?

1. The reaction realese heat then detalH = - 56.6kj
detalH(o2) =0
==>detalH(react)= 2*detalH(NO2) - 2*detalH(NO)
-56.6 + 2*90.4 = 2*detalH(NO2) ==>

3. a+b -->C  k=[c]/([a])

    2C--> 2a + 2b   k'= ([a]^2*^2)/[c]^2

==> k' = 1/k^2=1/0.123^2 = 66.08

[Donaldson Tan]

1) the reaction below releases 56.6kj of heat at 298k for each mole of NO2 formed at a constant pressure of 1 atm. what is the standard enthalpy of formation of NO2 given the standard enthalpy of NO is 90.4kj mol

2NO + O2 ---> 2NO2

You can visualise the question in this manner:
1. N₂ + O₂ -> 2 NO
2. 2NO + O₂ -> 2NO₂
so total dH from step 1 to 2 is:
dH₁ = 2 dH_f,NO = 2 mol NO x 90.4kJ/mol NO = 180.6 kJ
dH₂ = 2 dH_r = 2 mol NO₂ x -56.6kJ/mol NO₂ = -113.2 kJ
dH = dH₁ + dH₂

In fact, steps 1 and 2 can be sum up to produce:
N₂ + 2O₂ -> 2NO₂
Hence, dH = 2 x dH_f,NO2

dH_f,NO2 = dH/2

2) a 200g of copper at 100 degrees celsius is dropped into 1000g of water at 25 degrees celsius. what is the final temp of the system?

specific heat of water is 4.18J and copper is 0.400 J

The final temperature (T) of the water and the copper block must be the same, else heat transfer will not stop. The above problem can be solved by using an energy balance, ie.

heat absorbed by water = heat lost by copper block.
m_waterCp_water(T-T_ini,water) = m_copperCp_copperr(T_ini,copper - T)
where m is mass, and Cp is the specific heat capacity.

3) if the equilibrium constant for A + B <===> C is 0.123, the equilibrium constant when 2C <===> 2A + 2B is?

1. A + B <===> C
K₁ = [ C ] / [ A ] [ B ]

2. 2C <===> 2A + 2B is?
K₂ = [ A ]² [ B ]² / [ C ]² = ( [ A ] [ B ] / [ C ] )² = ( [ C ] / [ A ] [ B ] )^-2 = (K₁) ^-2