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CHEM FINAL TOMORROW AND I NEED HELP IN THESE REVIEW QUESTION!?
1) When 3.00 g potassium carbonate (K2CO3 ) was mixed with 20.0 mL of hydrochloric acid (HCl, 4.0M) in a calorimeter, the temperature raised 3.0 oC.
a. Write down the balanced reaction equation between K2CO3 and HCl.
b. Calculate the enthalpy change (∆H) of the reaction for per mole potassium carbonate. Assume the specific heat of all solutions are 4.18 J/g.oC and all solutions have a density =1.0 g/mL.
2) The stock solution contains Sr (10 mg/L), Mg (5 mg/L) and K (20mg/L). A student use 2.0 mL of the stock solution to make 50.0 ml of diluted solution.Calculate the concentration of Sr, Mg and K in the diluted solution.
3) Use Hess’s Law to find the reaction enthalpy for the following reaction:
N2 + 2O2 -------> 2NO2 ∆H =?
From N2 + O2 --------> 2 NO ∆H1 = 180kJ
2NO + O2 --------> 2 NO2 ∆H2 = -112kJ
1 Answer
- 10 years agoFavorite Answer
hey,....
I think we might be in the same class... b/c I have the same final practice questions, I can tell you the answer to your 3rd question.
you have to basically "add and cancel " the reactions. your final goal is from N2 + O2 --------> 2 NO & 2NO + O2 --------> 2 NO2 get N2 + 2O2 -------> 2NO2.
so you cancel whatever is repeated in each side. 2NO2 from the right side is cancelled with 2NO2 from the left, and u r left with N2 + 2O2 -------> 2NO2.
and since what you did was add the two reactions, you also have to add their ∆H respectively.
180kj+-112kj = 68 kj. and that is the answer :)
