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- A 2.74-g sample of a substance suspected of being pure gold is warmed to 72.1 °C and submerged into 15.2 g of water initially at 24.7 °C. The final temperature of the mixture is 26.3 °C. What is the heat capacity of the unknown substance? Could the substance be pure gold?
Problem 7
Problem 33
Convert between energy units. a. 534 kWh to J b. 215 kJ to Cal c. 567 Cal to J d. 2.85 × 103 J to cal
Problem 34a,b,d
Convert between energy units. a. 231 cal to kJ b. 132×104 kJ to kcal d. 2.88×104 J to Cal
Problem 34c
Convert between energy units. c. 4.99 × 103 kJ to kWh
Problem 35
Suppose that a person eats 2387 Calories per day. Convert this amount of energy into each unit. a. J b. kJ c. kWh
Problem 36a,b
A particular frost-free refrigerator uses about 745 kWh of electrical energy per year. Express this amount of energy in each unit. a. J b. kJ
Problem 36c
A particular frost-free refrigerator uses about 745 kWh of electrical energy per year. Express this amount of energy in each unit. c. Cal
Problem 37
Which statement is true of the internal energy of a system and its surroundings during an energy exchange with a negative ΔEsys? a. The internal energy of the system increases and the internal energy of the surroundings decreases. b. The internal energy of both the system and the surroundings increases. c. The internal energy of both the system and the surroundings decreases. d. The internal energy of the system decreases and the internal energy of the surroundings increases.
- During an energy exchange, a chemical system absorbs energy from its surroundings. What is the sign of ΔEsys for this process?
Problem 38
Problem 39a
Identify each energy exchange as primarily heat or work and determine whether the sign of ΔE is positive or negative for the system. a. Sweat evaporates from skin, cooling the skin. (The evaporating sweat is the system.)
Problem 39b
Identify each energy exchange as primarily heat or work and determine whether the sign of ΔE is positive or negative for the system. a. Sweat evaporates from skin, cooling the skin. (The evaporating sweat is the system.) b. A balloon expands against an external pressure. (The contents of the balloon is the system.) c. An aqueous chemical reaction mixture is warmed with an external flame. (The reaction mixture is the system.) Identify energy exchanges as primarily heat or work. Determine whether the sign of E is positive or negative for the system.
Problem 40
Identify each energy exchange as primarily heat or work and determine whether the sign of ΔE is positive or negative for the system. Identify each energy exchange as primarily heat or work. a. A rolling billiard ball collides with another billiard ball. The first billiard ball (defined as the system) stops rolling after the collision. b. A book falls to the floor. (The book is the system). c. A father pushes his daughter on a swing. (The daughter and the swing are the system). Identify each energy exchange as primarily heat or work.
Problem 41
A system releases 622 kJ of heat and does 105 kJ of work on the surroundings. What is the change in internal energy of the system?
Problem 42
A system absorbs 196 kJ of heat and the surroundings do 117 kJ of work on the system. What is the change in internal energy of the system?
- The gas in a piston (defined as the system) warms and absorbs 655 J of heat, while performing 344 J of work on the surroundings. What is the change in internal energy for the system?
Problem 43
Problem 44
The air in an inflated balloon (defined as the system) warms over a toaster and absorbs 115 J of heat. As it expands, it does 77 kJ of work. What is the change in internal energy for the system?