Chemistry Standard 7b

Chemistry Standard 7b: Students know chemical processes can either release(exothermic) or absorb (endothermic) thermal energy

The term exothermic describes a process or reaction that releases energy usually in the form of heat, but also in the form of light(flame, explosion, spark), electricity(battery), or sound. Chemical exothermic reaction are generally more spontaneous than endothermic reaction. In a thermochemical reaction that is exothermic, the heat is placed on the products of the reaction.

The opposite process is endothermic process which absorbs energy in the form of heat. Chemical endothermic reaction need heat to be performed. In a thermochemical reaction that is endothermic, the heat is placed on the reactant side.

Some examples of exothermic processes:

• freezing water
  
• condensing water vapor
  
• combustuin of fuels such as woods, coal and oil
  
• mixing alkalis and acids

Some examples of endothermic processes:

• melting ice cube
  
• evaporating liquid water
  
• converting frost to water vapor(melting, boiling and evaporation in general are endothermic processes )

exothermic reaction video

endothermic reaction video

making play-dough

Materials:

• 1 cup of flour


• 1 cup of water


• 1/2 cups of salt


• 1 table spoon of oil


• food color

Procedures:

1. Put flour, water, salt, and oil in the pan and mix them together.


2. On low temperature, put food color and stir them together


3. when the mixture becomes solid, turn off the burner so it can be cool enough to touch

Tips:

• sit the mixture on low temperature


• don't go to burner too close


• watch your hand when you stir the mixture

Science:

In play dough compound, surfactant combines with lubricant to reduce stickiness

photocredit: Theresa Anselmo

Bending Glass

I bent and twisted the glass today.

Tips:

• Don't bent the glass back and forth. It will make glass break.
• place the glass closely on the burner. It might take time if you place it too high.
• wear goggles and gloves for your safety
• Use two holders when ypu bend the glass

Science:

Glass is a visco-elastic material whose mechanical properties change very rapidly over a small temperature. so even though there isn't very high temperature. glass easily bends.

Photocredit: Kayla Jonansen

toothpick in the balloon

I stuck the toothpick in the balloon

Tricks:

• the smaller balloon you have, it's easier than bigger ones
• Use sharp toothpick so that can go into the balloon easily
• put vaseline on top of the balloon so it can make it smooth
• Stuck the toothpick on the very top of the balloon where has thickest rubber

Science:

Because of balloon's flexibility, balloon easiliy pops. But if you try on the top, rubber can easily move. so if there is more rubber, it's easier to stuck the sharp objects.

photocredit: Theresa Anselmo

Mills Canyon Field Trip

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