MasteringChemistry: CH 5 HWK-Google Chrome a Secure https//session.masteringchem

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MasteringChemistry: CH 5 HWK-Google Chrome a Secure https//session.masteringchemistry.com/myct/itemView?assignmentProblemiD-91561085& offset-prev CH5HWK Problem 5.44 with feedback 2 of 159 Partc Constants Periodic Table For a given sample of CH, OH the enthalpy change during the reaction is 82.7 kJ What mass of methane gas is produced? Express the mass to three significant digits with the appropriate units. Consider the following reaction You may want to reference Pages 179- 181) Section 54 while completing this problem alue Units Submit Part D How many kilojoules of heat are released when 38 4 g of CH(g) reacts completely with 02(s) to form CH,OH(g) at constant pressure? Express heat to three significant digits with the appropriate units Value Units Submit O Type here to search 254 PM ^1/14/2018

Explanation / Answer

Part D

We know that 2 moles of CH4 take 252.8 KJ so lets divide this by 2

252.8 / 2 = 126.4 KJ/mol

We know that we needed 82.7 KJ so

82.7 KJ / 126.4 KJ / mol = 0.654 moles of Methane are produced

molar mass of methane is 16 g/gmol so

mass = moles * molar mass = 0.656 * 16 = 10.468 grams

Part D

for this reaction we must inverse the chemical equation by doing this the enthalpy will have the same numerical value but with a different sign, it will be negative

lets find the moles of methane

n = mass / molar mass, where n is the number of moles

n = 38.4 / 16 = 2.4 moles of methane

we know that 1 mole of methane requires 126.4 KJ so

2.4 mole * 126.4 KJ / mol = 303.36 KJ will be released

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