Temperature and heat transfer were the topics discussed this w

Temperature and heat transfer are interesting topics. Several experiments can be done to help understand temperature, heat, and thermal energy. The ideal gas law, PV=nRT, expresses the relationship between the pressure, the Kelvin temperature, the volume, and the number of moles of the ideal gas. An ideal gas is a model for other gases if the other gases have low density (molecules are far apart). An ideal gas cannot be liquefied because the molecules must stick together. A real gas can exist as a liquid by decreasing the volume and increasing the pressure. This is shown in the graph below.

Temperature is the degree of hotness or coldness. Heat is the flow of thermal energy. Thermal energy (TE) is the random molecular kinetic energy in a thermal system. TE can also be defined as the motion of molecules in a thermal system. Random motion distinguishes thermal energy. The molecules of a ball are in coordinated linear motion when a ball is thrown. My classmate, Dawn Hurley, has a web page that discusses kinetic theory in more detail.
Rate of Equilibrium

I have conducted a few experiments with a calibrated electronic sensor, LoggerPro, and a thermometer. I measured how long it took for the electronic probe to reach equilibrium when immersed in water. I predicted it would take 25 seconds for the probe to reach equilibrium in ice water (0^oC). It actually took 55.5 seconds. The temperature probe/computer calibration was slightly off because the temperature at equilibrium was -0.622^oC instead of 0^oC. When the probe was taken out of the ice water, it took 350 seconds to reach equilibrium in the air at 16.85^oC. When analyzing this experiment, I concluded that the probe can become colder much faster than it can become warmer because the probe must absorb heat from the air.

Actually, the rate of temperature change depends on the number of molecular contacts per second. The water molecules are more dense than the air molecules and allow for a higher rate of thermal energy transfer (large molecular contact/sec). The air is less dense, so not as much molecular contact/sec occurs. Hence, the probe warms up slowly (slow TE transfer) when placed in the air. The energy lost by the warm air is gained by the cold air.

The temperature of styrofoam, wood, and metal was measured when the objects were at room temperature. All three objects had about the same temperature of 20^oC. The metal felt colder because metal is a good thermal conductor. It conducts heat away from the body (fingers) making the metal feel colder than the wood or styrofoam. My classmate, April Morgan, also describes the importance of thermal conductors on her web page.

The diagram below, which shows how the heat transfer experiment was conducted, demonstrates how the thermal energy in Joules is related to the temperature rise for water. The pulse length was 2 seconds. The heater produced 200 Watts. (1Watt=1J/s) 400 J/pulse was calculated by multiplying 200 J/s * 2 seconds. We used 179.3 g of water.

The computer, connected to the relay box and the calibrated probe, graphed the temperature vs. the number of

pulses. The reciprocal of the slope of the temperature vs. the number of heat pulses graph told us how many

A standard value told us that 4.19 Joules heat 1 g of water 1^oC. The percent error between our experimental data (4.45J/g/^oC) and the standard (4.19J/g/^oC) is 6.23%. This error can be attributed to the heat escaping into the air or the cup absorbing some of the heat. The calculations are shown below.