Problem 8.132 Part A Write a balanced equation for the reaction of potassium met
ID: 523067 • Letter: P
Question
Problem 8.132
Part A
Write a balanced equation for the reaction of potassium metal with water.
Write a balanced equation for the reaction of potassium metal with water.
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Part B
Use the data in Appendix B in the textbook to calculate H for the reaction of potassium metal with water.
Express your answer using four significant figures.
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Part C
Assume that a chunk of potassium weighing 8.05 g is dropped into 400.0 g of water at 26.5 C. What is the final temperature of the water if all the heat released is used to warm the water?
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Part D
What is the molarity of the KOH solution prepared in part (c)?
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Part E
How many milliliters of 0.665 M H2SO4 are required to neutralize it?
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K(s)+2H2O(l)K(OH)2(s)+H2(g) 2K(s)+2H2O(l)2KOH(s)+H2(g) 2K(s)+2H2O(l)2K+(aq)+2OH(aq)+H2(g) K(s)+H2O(l)K+(aq)+OH(aq)+H+(aq)Explanation / Answer
1.the reaction is 2K+2H2O(l)----->2KOH (aq)+ H2(g)
2. Enthalpy of formation data ( Kj/mole): KOH=-482.37, H2O=-285.83, K=0 and H2=0
standard enthalpy of reaction =2* enthaly of formatino of KOH+1* enthalpt of formation of H2 - {2* enthalpy of formatino of K+ 28enthalpt of formatino of water liquid}, 2,1,2 and 2 are coefficients of KOH,H2, K and KOH in the reaction.
=2* -482.37+2*285.83=-393 Kj/mole
moles of potasium in 8 gm =mass/molar mass = 8/39= 0.205
enthalpy change in 8 gm =-393*0.205 Kj=80.5 Kj= -80.5*1000 joules.This heat is taken by water
heat taken by water= mass* specific heat* temperature difference= 400*4.184*(T-26.5)= 80.5*1000
T-26.5=48.1
T= 48.1+26.5= 74.6 deg.c
mass of water= 400 gm, volume of water= mass/density, density= 1 g/cc, volume of water= mass/density= 400/1= 400ml =400/1000 L=0.4L
molarity = moles/Volume= 8/(39*0.4)= 0.5128M
The reaction between KOH and H2SO4 is 2KOH+ H2SO4------->K2SO4+H2O
moles of KOH= 8/39=0.205, moles of H2SO4 as per the reaction = 0.5 times H2SO4= 0.5* 0.205= 0.1025 moles
Volume of H2SO4(l) =moles sof H2SO4/molarity =0.1025/0.665=0.1541 L= 0.1541*1000=154.1 ml