14 An unknown mass of each of the following substances, initially at 21.0 C, abs

Question

14

An unknown mass of each of the following substances, initially at 21.0 C, absorbs 1950 J of heat. The final temperature is recorded as indicated. Find the mass of each substance.

Part A

a. Pyrex glass (Tf= 55.7 C)

Express your answer using two significant figures.

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Part B

sand (Tf= 62.0 C)

Express your answer using two significant figures.

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Part C

ethanol (Tf= 44.2 C)

Express your answer using two significant figures.

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Part D

water (Tf= 32.4 C)

Express your answer using two significant figures.

Explanation / Answer

Q = m c T
Q = quantity of heat in joules (J)
m = mass of the substance acting as the environment in
grams (g)
c = specific heat capacity (4.19 for H2O) in J/(g oC)
T = change in temperature = Tfinal - Tinitial in oC

Part A (specific heat capacity of pyrex glass=0.753 J/(g oC) )

m x (55.7 -21 ) x 0.753 = 1950

mass of pyrex = 74.629 gm

Part B(specific heat capacity of sand = 1.381 J/(g oC) )

m x (62 -21 ) x 1.381 = 1950

mass of sand = 34.439 gm

Part C (specific heat capacity of ethanol =2.460 J/(g oC) )

m x ( 44.2 - 21 ) x 2.46 = 1950

mass of ethanol = 34.167 gm

Part C (specific heat capacity of water = 4.184 J/(g oC) )

m x ( 32.4 - 21 ) x 4.184 = 1950

mass of water = 40.882 gm

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