Joules and calories

At one time or another, all of us have tangled with problems of units, but generally these decrease in severity and frequency with experience. Advanced students juggle kilograms and grams, centimeters and angstroms, joules and calories, and rarely fumble in the process. Electrical units are sometimes more troublesome. 

Suppose a 10.00-kg mass drops through a height difference of 3.00 m, and the resulting work is used to turn a paddle in 200.0 g water, initially at 15.00°C. The final water temperature is found to be 15.35°C. Assuming that the work done is used entirely to increase the water temperature, calculate the conversion factor between joules and calories. 

In order to convert the results obtained by the electrical heating method into calories, it is necessary to know the relationship between joules and calories. That there is such an exact connection is really an aspect of the first law of thermodynamics ( 6a), which will be tacitly assumed for the present. Because of a slight uncertainty, of about two parts in 10,000, concerning the relationship between the standard (K5 ) calorie, as defined in 3d, and the int. joule ( 3b), a defined calorie,... 

A 5.63-g sample of solid goid is heated from 21 °C to 32 °C. How much energy (in joules and calories) is required ... 

We want to determine the amount of energy (units of joules and calories) to increase the temperature of 1.3 g, of iron from 25° C to 46° C. 

We need the specific heat capacity of iron and the conversion factor between joules and calories. 

REALITY CHECK The units (joules and calories) are correct, and the answer is reported to the correct number of significant figures (two). 

A calorimeter is used to measure the heats of chemical reactions. The common imits for heat are joules and calories. 

The Sl-derived unit for energy is the joule (pronounced jool, rhyming with tool, and abbreviated J). Another unit for heat energy, which has been used for many years, is the calorie (abbreviated cal). The relationship between joules and calories is... 

Since joules and calories are rather small units, kilojoules (kJ) and kilocalories (kcal) are used to express heat energy in many chemical processes. The kilocalorie is also known as the nutritional, or large, Calorie (spelled with a capital C and abbreviated Cal). In this book, heat energy will be expressed in joules. 

Note that the product of volume and pressure gives units of energy (i.e., joules and calories). 

Use the heat equation to calculate the energy, in joules and calories, for each of the following (see Table 3.11) ... 

How much heat does a 23.0-g ice cube absorb as its temperature increases from — 17.4 C to 0.0°C Give the answer in both joules and calories. 

---