20. Consider the reaction: C + o, -co, AH-393 kJ How many grams of carbon must b

Question

20. Consider the reaction: C + o, -co, AH-393 kJ How many grams of carbon must be burned to release 275 kJ of heat? a. 22.3 g b. 8.4g c. 12.0g d. 17.1g 21. Given the following: Find H for the reaction : 2S + 30,-o 2 so, a. 791 kJ b. - 495 kJ c. 495 kJ d. 99 kJ 22. H, for A403 is-1670 kJ. Which of the following equations does this quantity refer to? a, Al,03-2A1+ ½o, c. 4 Al + 2 O3 -2 AI2O3 23. A piece of copper with a mass of 218 g has a heat capacity of 83.9 JI°c. What is the specific heat of copper? a. 0.385 J/g C b. 2.60 Jig C c. 1.32 Jig c d. 24.5 J/g C 24. In the termAH', the' refers to: a. degrees b. zero temperature c. pressure d. standard conditions :-393 kJ AH=-786 kJ. could also be + 02-Co, 25. The reaction: C written as 2C + 202-2C02 This is an example of a. Dalton's Law b. Hess's Law c. Gay-Lussac's Law d. Charles' Law

Explanation / Answer

Q20

1 mol = 393

x mol = 275

mol = 275/393 = 0.6997 mol

then

mass of C = mol*M;W = 0.6997*12

mass of C = 8.3964

chjoose b, m = 8.4 g

Q21

apply hess law

multipl RXN 1 by 3, then, multiply rxn 2 by 3/2

2S + 2O2 = 2SO2 H = 2(-297) = -594

SO2 + O2 = SO3 H =(-198)

add all

HTotal = -594+-198= -792 kJ

nearest answer is A

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