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For example, the energy required to raise the temperature of 0.500 kg of water by 3.00°C 3 J. Note that when the temperature in- creases, Q and #T are taken to be positive, and energy transfers into the system. When the Specific heat varies with temperature. However, if temperature intervals are not too great, the temperature variation can be ignored and c can be treated as a constant. 2 For example, the specific heat of water varies by only about 1% from 0°C to 100°C at Measured values of specific heats are found to depend on the conditions of the ex- periment. In general, measurements made in a constant-pressure process are different It is interesting to note from Table 20.1 that water has the highest specific heat of com- mon materials. This high specific heat is responsible, in part, for the moderate tempera- Conservation of Energy: Calorimetry One technique for measuring specific heat involves heating a sample to some known x , placing it in a vessel containing water of known mass and temperature T w ' T x , and measuring the temperature of the water after equilibrium has been reached. This technique is called calorimetry, and devices in which this energy trans- fer occurs are called calorimeters. If the system of the sample and the water is iso- lated, the law of the conservation of energy requires that the amount of energy that 3 S E C T I O N 2 0 . 2 • Specific Heat and Calorimetry 609 2 The definition given by Equation 20.3 assumes that the specific heat does not vary with temperature over the interval #T ! T f & T i . In general, if c varies with temperature over the inter- val, then the correct expression for Q is 3 For precise measurements, the water container should be included in our calculations because it also exchanges energy with the sample. Doing so would require a knowledge of its mass and Q ! m
" T f T i c dT. Quick Quiz 20.1 Imagine you have 1 kg each of iron, glass, and water, and that all three samples are at 10°C. Rank the samples from lowest to highest tempera- Quick Quiz 20.2 Considering the same samples as in Quick Quiz 20.1, rank them from least to greatest amount of energy transferred by heat if each sample in- ▲ PITFALL PREVENTION 20.4 Energy Can Be Transferred by Any We will use Q to represent the |