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febbie22

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## Homework Statement

1 kg of air at a pressure of 100 kPa occupying a volume of 0.025 m3 is

compressed to a pressure of 150 kPa according to the law

pv1.3 = constant.

Determine:

(i) Work done on or by the gas; (6)

(ii) Change in internal energy of the gas; (6)

(iii) Heat received or rejected by the gas; (4)

Take Cv = 0.718 kJ/kg K, Cp = 1.005 kJ/kg K

## Homework Equations

In attachment the password is exam

## The Attempt at a Solution

I think i can do the first part fine:

W= ((100*10^3) * 0.025 - (150*10^3) * 0.0183) / -0.3

= 816.67

Its the second part that i don't get as it asks for the change in internal energy before the heat received

is there a equation to calculate the internal energy as there is one here:

U2-U1= Q + W

but i would need to work out Q before U2-U1

any help would be much appreciated