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#### elgenia

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##### Homework help
« on: February 01, 2012, 02:21:01 PM »

I having some difficulties with some problems in my Chemistry Nyb class and need help.

4. Consider the following reaction.
2 HCl(aq) + Na2CO3(aq)--->2 NaCl(aq) + H2O(l) + CO2(g)
The following reaction occurs in a solvent of water (s = 4.184 J/gK, d = 1.00 g/mL) which can
be considered as part of the reaction’s surroundings. When 50.0 mL of 2.00 M HCl and 50.0
mL of 2.00 M Na2CO3 (both initially at 23.5 °C) are mixed, the temperature of the final
mixture is 28.3 °C. The reaction takes place in a room whose temperature is constant at 23.5
°C and the container in which is occurs absorbs a negligible amount of heat. Calculate q, w,
and ΔE for this reaction per mole of CO2 produced. What is the value of ΔHrxn calculated in
kJ/mol?
(Hints: Remember that the carbon dioxide leaves the solution and expands into the room. )
5. Exactly 1.5 g of a liquid fuel is burned to produce gaseous products under conditions of
constant pressure and then under conditions of constant volume. In measurement A the
reaction produces 25.9 kJ of heat, and in measurement B the reaction produces 23.3 kJ of heat.
Which measurement, A or B, corresponds to conditions of constant pressure? Which one
corresponds to conditions of constant volume? Explain.

6. When a barbeque burns propane the overall reaction is the following.
C3H8(g) + 5 O2(g) ---> 3 CO2(g) + 4 H2O(g)
Use the following information to determine the mass of propane (44.10 g/mol) that must be
burned to provide enough energy to heat a pot containing 4.00 kg of water from 24.5 °C to 99.0
°C. Assume all heat from the combustion of propane is transferred to the water and that the
combustion reaction occurs at constant pressure.
The standard heat of formation of propane gas at 298 K is -103.8 kJ/mol.
The standard heat of formation of carbon dioxide gas at 298 K is -393.5 kJ/mol.
The standard heat of formation of liquid water at 298 K is -285.8 kJ/mol.
The standard heat of vaporization of water is 44.0 kJ/mol.
The specific heat capacity of water is 4.186 J/molK.
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#### elgenia

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##### Re: Homework help
« Reply #1 on: February 02, 2012, 04:16:32 AM »

In number 6, I found the number of moles of H20 which gives 2,22 x 10-4 mol but I do not know where to go from there.

In number 4,I found the q of the solution which gives me 2008,32 J and I am stuck.
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#### fledarmus

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##### Re: Homework help
« Reply #2 on: February 02, 2012, 04:36:12 AM »

For number 6, what does the heat capacity of water tell you?
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#### elgenia

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##### Re: Homework help
« Reply #3 on: February 02, 2012, 07:28:37 AM »

It helps us find Q
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#### fledarmus

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##### Re: Homework help
« Reply #4 on: February 02, 2012, 08:17:33 AM »

And if all of the heat given off by the reaction is going into your (how much?) water and is raising the temperature (how much?) degrees, then how much heat is your reaction giving off?
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