Convert be wee a. 231 cal to kjergy units. b. 122 x 10 kJ to KWh c. 2.88x 10+ J

Question

Convert be wee a. 231 cal to kjergy units. b. 122 x 10 kJ to KWh c. 2.88x 10+ J to Cal 35. During an energy exchange, a chemical system absorbs energy from its surroundings, what is the sign of , for this process? why? Explain. 36. How much heat is required to warm 1.5 kg of sand from 25'C to 100*C? 37. Determine whether each process is exothermic or endothermic and indicate the sign a. Dry ice evaporating b. A sparkler burning c. Water condensing from steam 38. What mass of natural gas (CH4) must burn to emit 267 kJ of heat? CH4 (g) + 2O2(g) CO2(g) + 2H2O(g) dH.mF-802.3k J

Explanation / Answer

34.

a. 1 cal =4.18 x 10 ^(-3) kJ

so for 231 cal = 231 x 4.18 x 10^(-3) kJ=0.96558 kJ

b. 1 kJ =0.000277778 kWh

so for 122 x 10^(4) kJ = 122 x 10^(4) x 0.000277778 kWh= 338.88916kWh

c. 1 J = 0.239006 cal

2.88 x 10^(4) J= 2.88 x 10^(4) x 0.239006 cal= 6883 cal

35. As the system absorbs energy from the surrounding so its energy will increase that means its final energy will be larger that that of the innitial. So Delta E will naturally be positive.

36. Energy required to warm water from T1 to T2 is given by Delta E = mCp(T2-T1)

Cp=specific heat of water=4.18 J/Kg.K, mass=1.5 kG, T2-T1 =100-25=75 Degree celcius

So Delta E= 1.5 x 4.18 x 75 J=470.25 J

37.

a. Dry ice eveporating= for evaporation requires heat so it is endothermic process(absorption of heat)

b.A sparkler burning= sparkling involves releasing the heat so it is exothermic.

c. Water condensing from steam= While condensing it is going into liquid phase from gas phase, thus naturally it will lose heat and so exothermic process.

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