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Topic: Stuck on how to solve these 2 problem! {calorimetry, enthalpy}  (Read 1921 times)

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Offline Superboy92

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Stuck on how to solve these 2 problem! {calorimetry, enthalpy}
« on: October 16, 2012, 02:06:18 AM »
1. 15.3 g of sodium nitrate was dissolved in water in a calorimeter and the temperature fell from 25.00 to 21.56. If the heat capacity of the solution and the calorimeter is 1071 J/C, what is the enthalpy change when 2.00 mole of sodium nitrate dissolves in water?

2. Calculate the enthalpy of formation for acetic acid from the following data:
CH3COOH (l) + 2O2 (g) --> 2 CO2 (g) +2 H2O (l) -871 kJ
C (graphite) + O2 (g) --> CO2(g) -394 kJ
H2 (g) + 1/2 O2 (g) --> H2O (l) -286 kJ


Ok, so for problem one, I started with (1071)(21.56-25.00)(15.3g) = -x(4.184)(21.56-0)(18.016) and I'm not sure if I'm doing it right? solved for x I got 34.7 g and I'm not sure where/what to do from there.

Can someone please show me the right way to do it and show the steps so I can understand and learn on how to solves these 2 problems?

For problem 2, I don't know how to start it

*MOD Edit -- add useful title*
« Last Edit: October 16, 2012, 08:13:41 AM by Arkcon »

Offline curiouscat

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Re: Stuck on how to solve these 2 problem!
« Reply #1 on: October 16, 2012, 02:30:21 AM »


2. Calculate the enthalpy of formation for acetic acid from the following data:
CH3COOH (l) + 2O2 (g) --> 2 CO2 (g) +2 H2O (l) -871 kJ
C (graphite) + O2 (g) --> CO2(g) -394 kJ
H2 (g) + 1/2 O2 (g) --> H2O (l) -286 kJ

2 x R2 + 2 x R3 - R1

Offline curiouscat

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Re: Stuck on how to solve these 2 problem!
« Reply #2 on: October 16, 2012, 03:04:00 AM »



Ok, so for problem one, I started with (1071)(21.56-25.00)(15.3g) = -x(4.184)(21.56-0)(18.016) and I'm not sure if I'm doing it right? solved for x I got 34.7 g and I'm not sure where/what to do from there.

Show units in the eqn.

you've multiplied J/C * C * gm

J*gm is not a sensible unit.

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