2C 2 H 6 (g) + 7O 2 (g) ? 4CO 2 (g) + 6H 2 O (g) ?H = -1560 kJ How much energy (

Question

2C2H6 (g) + 7O2 (g) ? 4CO2(g) + 6H2O (g) ?H = -1560 kJ

How much energy (in kJ) is released if 16.9 g of ethane ( 30.07 g/mol) undergoes combustion?

(Give your answer as a positive number, since you cannot release negative energy.)

What volume (in mL!!!) of 2.28 M HCl is required to react with 4.05 g of zinc (65.41 g/mol) according to the following reaction?

Zn(s) + 2 HCl (aq) ? ZnCl2(aq) + H2(g)

2 N2(g) + O2(g) ? 2 NO2(g)

In a cylinder with a moveable piston (pressure remains constant) the above reaction occurs. If both the temperature drops and the volume decreases during the reaction, what are the signs of q and w? Negative or positive.

q   

w

Energy change is the sum of heat and work: ?E = q + w. Work is calculated by: w = -P?V

What is the change in energy (in joules) if a reaction absorbs 77.7 J of heat and increases in volume from 0.250L to 0.750L at a constant pressure of 1.161 atm? Please include the correct sign with your numerical result.

(Note: Make sure your units are consistent when combining energy terms. The conversion factor you need is: 1 L

Explanation / Answer

2 moles of ethane gives off 1560 kJ , means

1 mole of ethane gives: 780 kJ of energy.

No of moles in 16.9 g of ethane = 16.9 g/(30.7 g/mol) = 0.55 moles

therefore energy released by 16.9 g ethane = 429.38 kJ

b) number of moles in 4.05 g of zinc (65.41 g/mol) = 0.062 moles

each mole of Zn requires 2 moles of HCl. therefore, nuumber of moles of HCl required by 0.062 moles of zinc = 0.124

MV=0.124

2.28*V=0.124

V=0.05438 L = 54.38 mL

c) work done is positive, since w=-pdV and, dV=-ve.

since temperature decreases, and work is positive, q is positive.

d) E= q+w

= 77.7J - 1.161*0.5 * 101.3 J = 18.89J

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