CHEM 130 3) Molten ionic compounds are used to store heat. How many kJ of energy

Question

CHEM 130 3) Molten ionic compounds are used to store heat. How many kJ of energy are A. Bazel Fall 2007 released when 8.37 kg of NaCI solidifies at its melting point? H 4) How many kilojoules are required to melt 0.135 kg of ice? op 5) Does steam cause more severe burns than hot water does? Explain. SHL Compare 3.00 g of 100.0 °C water cooling to 60.0 °C with 3.00 g of 100.0 oC steam condensing then cooling to 60.0 °C. How much energy must be removed to cool 21 g of steam at 130.0 °C to ice at -75 °C? 6) SHs SHI SHg AHrusion AHvap NPB NMP 519 13,100 20 2.03 4.18 2.0 334 2,266 NaCI

Explanation / Answer

Q3

Hmelting of NaCl --> 519 J/g

if m = 8.37 kg = 8370 g

Qtotal = mass*Hmelt = 8370*519 = 4344030 J required = 4344.030 kJ

Q4

m = 0.135 kg of ice --> 135 g of ice

Hfussion = 334 J/g

Qtotal = mass*Hfussion = 135 * 334 = 45090 J = 45.090 kJ

Q5

heat of water = m*C*(Tf-Ti) = 3*4.184(60-100) = -502.08 J

heat steam = mcond + m*C*(Tf-Ti) =  -3*2266 +  3*4.184*(60-100) = -7300.08 J

steam requires much more energy to change phase

Q6

We are given a solute + solvent. In this case is an ACID + WATER respectively.

They will break solute-solute and solvent-solvent interacitons in order to yield either a positive or negative value of solvent-solute interaction energy. This is called enthalpy/heat of solution/solvation.

For

Total Heat from Ice to Vapor

We require 2 type of heat, latent heat and sensible heat

Sensible heat (CP): heat change due to Temperature difference

Latent heat (LH): Heat involved in changing phases (no change of T)

Then

Q1 = m*Cp ice * (Tf – T1)

Q2 = m*LH ice

Q3 = m*Cp wáter * (Tb – Tf)

Q4 = m*LH vap

Q5 = m*Cp vap* (T2 – Tb)

Note that Tf = 0°C; Tb = 100°C, LH ice = 334 kJ/kg; LH water = 2264.76 kJ/kg.

Cp ice = 2.01 J/g°C ; Cp water = 4.184 J/g°C; Cp vapor = 2.030 kJ/kg°C

Then

Q1 = 21*2.01 * (0 – -75)

Q2 = 21*334

Q3 = 21*4.184 * (100 – 0)

Q4 = 21*2264.76

Q5 = 21*2.03* (130– 100)

QT = Q1+Q2+Q3+Q4+Q5 = 3165.75 +7014 + 8786.4+47559.96+1278.9

QT = 67805.01 J must be REMOVED

Related Questions

Navigate

• Browse (All)
• Browse C
• Subjects

---