Thermochemistry Practice Calculations

Chemistry

HS/Science

Unit: 12 Lesson: 01

Name ______Date ______Class ______

Modern Chemistry • CHAPTER 17

HOMEWORK 17-3

Thermochemistry Practice Calculations

Use the appropriate formula and conversion factors from the STAAR Chemistry Reference Materials to do the following calculations. Use scientific notation, and consider significant figures. SHOW YOUR WORK!

1. Compare and contrast joules (J), calories (cal), and Calories (Cal).

2. Make the following conversions:

a. 1988 J = ______cal

b. 1.225 Cal = ______J

c. 765 cal = ______Cal

3. Under what conditions will heat to move from one object or system to another?

4. An average-size potato (about 200 g) has an energy value of 686,000 J. How many Calories will a man get if he consumes two potatoes?

5. Which material needs more energy to undergo a fifteen degree increase in temperature - a material with a higher specific heat or one with a lower specific heat? What factor, other than the type of materials, must you know before you can be sure of your answer to this question?

6. How much heat in joules is required to raise the temperature of 894 g of H2O from 23.5°C to 85.0°C?

7. Carbon tetrachloride was commonly used as an organic solvent until it was found to be carcinogenic. How much heat is required to raise the temperature of 10.35 g of CCl4 from 32.1°C to 56.4°C? The specific heat of CCl4 is 0.85651 J/g °C.

8. How many joules are needed to heat 692.0 g of nickel from 22.0°C to 318°C? (The cp of nickel is 0.4442 J/g °C.)

9. Heated bricks or blocks of iron were once used to warm beds. Suppose a 1.49 kg block of iron heated to 155°C was used one evening. How many joules of heat would be released as it cooled to room temperature, 22.0 C°? (The cp of iron is 0.4494 J/g °C.)

10. A 105 g sample of copper is exposed to 152 J of heat in an insulated container. How many degrees will the temperature of the copper sample increase (assuming no heat is lost)? The cp of copper is 0.38452 J/ g °C.