a) A system does work on the surroundings equal to 64 J and the change in energy

Question

a) A system does work on the surroundings equal to 64 J and the change in energy is -213 J. Calculate the heat  J

b) If 6.40 kJ of heat is needed to raise the temperature of a sample of metal from 14°C to 28°C, how many kilojoules of heat will be required to raise the temperature of the same sample of metal from 31°C to 54°C?

c) If 137 J of heat is applied to a 34 g sample of mercury, how many degrees will the temperature of the sample of mercury increase?

d) What quantity of heat is required to raise the temperature of 57.4 g of gold from 27°C to 66°C?

e) For the reaction below H = -296 kJ per mole of SO2 formed.

S(s) + O2(g) SO2(g)

(1) Calculate the quantity of heat released when 1.45 g of sulfur is burned in oxygen.

(2) Calculate the quantity of heat released when 0.522 mol of sulfur is burned in air.

(3)What quantity of energy is required to break up exactly 4 mol of SO2(g) into its constituent elements?

Explanation / Answer

a)

we know that

Q =dU + E

given

dU = -213

W = 64

so

Q = -213 + 64

Q = -149 J

so

the heat is -149 J

b)

we know that

heat = mass x specific heat x temp change

so

Q = m x s x dT

now

So

Q1 = m1 x s1 x dT1

Q2 = m2 x s2 x dT2

in this case

mass and specific heat of metal does not change

so

Q2/Q1 = dT2/dT1

Q2 / 6.4 = ( 54-31) / ( 28-14)

Q2 = 10.514 kJ

so

10.514 kJ of heat is required to raise 31 C to 54 C

c)

we know that

Q = m x s x dT

also

specific heat of mercury = 0.14 J/g C

so

137 = 34 x 0.14 x dT

dT = 28.78

so

the temperature will increase by 28.78 C

d)

now

Q = m x s x dT

specific heat of gold = 0.129 J / g C

so

Q = 57.4 x 0.129 x ( 66-27)

Q = 288.78 J

so

the heat required is 288.78 J

e)

we know that

moles = mass / atomic mass

so

moles of S = 1.45 / 32 = 0.0453125

now

S + 02 --> S02

so

moles of S02 formed = moles of S reacted = 0.0453125

now

heat released = 296 x 0.0453125

heat released = 13.4125 kJ

so

13.4125 kJ of heat is released

2)

S + 02 ---> S02

we can see that

moles of S02 formed = moles of S reacted = 0.522

so

heat released = 296 x 0.522

heat released = 154.512

so

154.512 kJ of heat released

3)

given

S + 02 ---> S02 dH = -296

so

S02 ---> S + 02 dH = +296

we can see that

for 1 mol of S02 --> 296

for 4 mol of S02 ----> 296 x 4 = 1184

so

1184 kJ of heat is required to break up 4 mol of S02

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