1.4 Heat transfer, specific heat, and calorimetry  (Page 7/14)

How is heat transfer related to temperature?

Describe a situation in which heat transfer occurs.

When heat transfers into a system, is the energy stored as heat? Explain briefly.

The brakes in a car increase in temperature by $\text{Δ}T$ when bringing the car to rest from a speed v . How much greater would $\text{Δ}T$ be if the car initially had twice the speed? You may assume the car stops fast enough that no heat transfers out of the brakes.

On a hot day, the temperature of an 80,000-L swimming pool increases by $1.50\text{°}\text{C}$ . What is the net heat transfer during this heating? Ignore any complications, such as loss of water by evaporation.

To sterilize a 50.0-g glass baby bottle, we must raise its temperature from $22.0\text{°}\text{C}$ to $95.0\text{°}\text{C}$ . How much heat transfer is required?

The same heat transfer into identical masses of different substances produces different temperature changes. Calculate the final temperature when 1.00 kcal of heat transfers into 1.00 kg of the following, originally at $20.0\text{°}\text{C}$ : (a) water; (b) concrete; (c) steel; and (d) mercury.

Rubbing your hands together warms them by converting work into thermal energy. If a woman rubs her hands back and forth for a total of 20 rubs, at a distance of 7.50 cm per rub, and with an average frictional force of 40.0 N, what is the temperature increase? The mass of tissues warmed is only 0.100 kg, mostly in the palms and fingers.

A $0.250\text{-kg}$ block of a pure material is heated from $20.0\text{°}\text{C}$ to $65.0\text{°}\text{C}$ by the addition of 4.35 kJ of energy. Calculate its specific heat and identify the substance of which it is most likely composed.

Suppose identical amounts of heat transfer into different masses of copper and water, causing identical changes in temperature. What is the ratio of the mass of copper to water?

(a) The number of kilocalories in food is determined by calorimetry techniques in which the food is burned and the amount of heat transfer is measured. How many kilocalories per gram are there in a 5.00-g peanut if the energy from burning it is transferred to 0.500 kg of water held in a 0.100-kg aluminum cup, causing a $54.9\text{-}\text{°}\text{C}$ temperature increase? Assume the process takes place in an ideal calorimeter, in other words a perfectly insulated container. (b) Compare your answer to the following labeling information found on a package of dry roasted peanuts: a serving of 33 g contains 200 calories. Comment on whether the values are consistent.

Following vigorous exercise, the body temperature of an 80.0 kg person is $40.0\text{°}\text{C}$ . At what rate in watts must the person transfer thermal energy to reduce the body temperature to $37.0\text{°}\text{C}$ in 30.0 min, assuming the body continues to produce energy at the rate of 150 W? $\left(1\text{watt}=1\text{joule/second}\text{or}1\text{W}=1\text{J/s}\right)$

In a study of healthy young men JW Vezina, “An examination of the differences between two methods of estimating energy expenditure in resistance training activities,” Journal of Strength and Conditioning Research , April 28, 2014, http://www.ncbi.nlm.nih.gov/pubmed/24402448 , doing 20 push-ups in 1 minute burned an amount of energy per kg that for a 70.0-kg man corresponds to 8.06 calories (kcal). How much would a 70.0-kg man’s temperature rise if he did not lose any heat during that time?

A 1.28-kg sample of water at $10.0\text{°}\text{C}$ is in a calorimeter. You drop a piece of steel with a mass of 0.385 kg at $215\text{°}\text{C}$ into it. After the sizzling subsides, what is the final equilibrium temperature? (Make the reasonable assumptions that any steam produced condenses into liquid water during the process of equilibration and that the evaporation and condensation don’t affect the outcome, as we’ll see in the next section.)

Repeat the preceding problem, assuming the water is in a glass beaker with a mass of 0.200 kg, which in turn is in a calorimeter. The beaker is initially at the same temperature as the water. Before doing the problem, should the answer be higher or lower than the preceding answer? Comparing the mass and specific heat of the beaker to those of the water, do you think the beaker will make much difference?