#### Heat And Temperature

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Water, H2O, and hexane, C6H14, are commonly used as laboratory solvents because they have different physical properties and are able to dissolve different types of solutes. Some physical properties of water and hexane are listed on the table below.

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Thermal energy is absorbed as chemical reactions occur during the process of baking muffins. The batter for muffins often contains baking soda, NaHCO3(s), which decomposes as the muffins are baked in an oven at 200.°C. The balanced equation below represents this reaction, which releases CO2(g) and causes the muffins to rise as they bake. The H2O(ℓ) is released into the air of the oven as it becomes a vapor.

2NaHCO3(s) + heat → Na2CO3(s) + H2O(ℓ) + CO2(g)

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• A test tube contains a sample of solid stearic acid, an organic acid.
• Both the sample and the test tube have a temperature of 22.0°C.
• The stearic acid melts after the test tube is placed in a beaker with

320. grams of water at 98.0°C.

• The temperature of the liquid stearic acid and water in the beaker reaches 74.0°C.
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Carbon dioxide, CO2, changes from the solid phase to the gas phase at 1 atm and 194.5 K. In the solid phase, CO2 is often called dry ice. When dry ice sublimes in air at 298 K, the water vapor in the air can condense, forming a fog of small water droplets. This fog is often used for special effects at concerts and in movie-making.

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A sample of a substance is a liquid at 65°C. The sample is heated uniformly to 125°C. The heating curve for the sample at standard pressure is shown below.

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