CHE 105/110 Introduction to Chemistry - Exercises and Answers

1.

Give two definitions of work.

1.

Work is a force acting through a distance or a volume changing against some pressure.

3.

What is the work when a gas expands from 3.00 L to 12.60 L against an external pressure of 0.888 atm?

3.

−864 J

5.

What is the work when a gas contracts from 3.45 L to 0.97 L under an external pressure of 0.985 atm?

5.

248 J

7.

Like work, the sign on heat can be positive or negative. What is happening to the total energy of a system if heat is positive?

7.

When heat is positive, the total energy of the system is increasing.

9.

What is the heat when 55.6 g of Fe increase temperature from 25.6°C to 177.9°C? The heat capacity of Fe is in Table 2.1 "Specific Heats of Various Substances".

9.

3.80 × 10³ J

11.

What is the heat when 245 g of H₂O cool from 355 K to 298 K? The heat capacity of H₂O is in Table 2.1 "Specific Heats of Various Substances".

11.

−58,400 J

13.

It takes 452 J of heat to raise the temperature of a 36.8 g sample of a metal from 22.9°C to 98.2°C. What is the heat capacity of the metal?

13.

0.163 J/g·°C

15.

An experimenter adds 336 J of heat to a 56.2 g sample of Hg. What is its change in temperature? The heat capacity of Hg is in Table 2.1 "Specific Heats of Various Substances".

15.

43.0°C

17.

An unknown mass of Al absorbs 187.9 J of heat and increases its temperature from 23.5°C to 35.6°C. What is the mass of the aluminum? How many moles of aluminum is this?

17.

17.3 g; 0.640 mol