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Experiments that involve changing the temperature of a material and measuring that change are necessarily subject to energy transfers between that material or materials and the surrounding environment. A correction that must be employed in calorimetry to allow for heat transfer between a body and its surroundings. Also known as radiation correction. Heat-exchange device similar to a plate-and-frame filter press; fluids flow between the frame-held plates, transferring heat between them.
A flat plate against which something rests or is pressed. The rubber-covered roller of a typewriter against which paper is pressed when struck by the typebars.
The first law of thermodynamics is basically the law of conservation of energy. This means that energy can change form. The hot water that you use for this experiment contains heat, or thermal energy. When you used a stove, microwave, or hot plate to heat the water, you converted electrical energy into thermal energy. The total amount of energy in the universe is constant.
The energy can change form, but the total amount remains the same. Energy is conserved. The second law of thermodynamics states that the entropy, or disorder, of the universe always increases.
For purposes of this experiment, this means that heat always travels from a hot object to a cold object. Rather, the heat from the soup is melting the ice and then escaping into the atmosphere. In this experiment, the heat from the hot water is being transferred into the air surrounding the beaker of hot water. Newton's law of cooling applies to convective heat transfer; it does not apply to thermal radiation. Newton's law of cooling states that the rate of heat exchange between an object and its surroundings is proportional to the difference in temperature between the object and the surroundings.
Mathematically that is represented as:. There are 2 general solutions to this equation. If the temperature of the object, T, is greater than the temperature of the surroundings, T a , then:. If the ambient temperature, T a , is less than the temperature of the object, T, the solution to the equation is:.
The solution to the differential equation gives 2 exponential functions that can be used to predict the future temperature of the cooling object at a given time, or the time for an object to cool to a given temperature. In this experiment, a glass of hot water will cool to match the temperature of the surroundings, and the following equation will be used:.
Note: Details for deriving Equations 1 and 2 are found at the end of this article. Observe all standard lab safety procedures and protocols. Wear appropriate personal protective equipment PPE. This lab involves using a hot plate and hot water.
Wear safety glasses when heating and moving hot water, and use tongs or heat-resistant gloves to move the hot beaker. Turn off and disconnect the hot plate when heating is complete, and remember always to treat the surface of the hot plate as if it were hot. Repeat the procedure, measuring the temperature outside, of your ice bath, or in your refrigerator for T a. Use the same volume of hot water, starting at the same temperature.
Record the data in Table 1. This activity is a mathematical exercise. Apply Equation 2 to the data collected in Activity 1 in order to predict the temperature of the water at a given time. Temperature as a function of time depends on the variables C 2 , k, and T a.
If these values are known, then the temperature at any time, t, can be found simply by substituting that time for t in the equation. Or the time for an object to reach a certain temperature can be found by solving for t, and substituting T t for the given temperature.
Now use these 2 constants to predict the temperature at some future time, and use the data in Table 1 to verify the answer. Solving for t:. There are 2 general solutions for this equation. One solution is if the matter at temperature T is hotter than the ambient temperature T a. Since the expression on the left side of the equation is between absolute value bars, T — T a can either be positive or negative.
Equation 1 applies if the temperature of the object or substance, T, is greater than the ambient temperature T a ; Equation 2 applies if the ambient temperature is greater than the object or substance. What if the temperature of the atmosphere is warmer than the sample of matter?
Can you develop a procedure to test this equation? Start with a sample of cold water, and repeat the process in Activity 2. Try to predict how long it will take for the water to reach room temperature. We use cookies to provide you with a great user experience. By using our site, you accept our use of cookies. You can review our cookie and privacy policy here. Login or Register My Account Login or register now to maximize your savings and access profile information, order history, tracking, shopping lists, and more.
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