What's Hot? Year 10 Science 2012 Section 1: Energy in Chemical reactions.
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Transcript of What's Hot? Year 10 Science 2012 Section 1: Energy in Chemical reactions.
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What's Hot?Year 10 Science 2012
Section 1: Energy in Chemical reactions
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Energy and Chemical Reactions
Many chemical reactions release energy in the form of heat, light, or sound. These are exothermic reactions.
There are other chemical reactions that must absorb energy in order to proceed. These are endothermic reactions.
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Demonstration of exothermic and endothermic reactions
Record your observations stating whether the reactions are exothermic or endothermic
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Exothermic Reactions
Exothermic reactions may occur spontaneously. Exothermic reactions produce heat or may even be explosive.
An exothermic reaction is one which transfers heat energy to the surroundings
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• Magnesium + Hydrochloric acid
Gets hot
25o C 45o C
magnesium
Hydrochloricacid
Heatenergygivenout
Exothermic Reactions
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Examples of Exothermic reactions
• Skiers and mountain climbers often use hand warmers inside their gloves. These small heat packs rely on exothermic processes.
• Combustion is an example of an exothermic reaction
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Bunsen burners burn methane:
Cigarette lighters use butane to produce a flame:butane + oxygen carbon dioxide + water
Alcohols are also flammable, for example:ethanol + oxygen carbon dioxide + water
Chemistry is full of patternsWhat pattern do you see here?
Combustion
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Examples of exothermic processes
Change of stateWhen steam condenses into water, the water molecules lose energy and this energy is transferred to the surroundings. Similarly, when water freezes, the water molecules lose even more energy to the surroundings.
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Exothermic Examples• Chemical Reactionso A candle flameo Rusting irono Burning sugaro Glow stickso Fire crackers
• Physical processeso Some hand warmerso Some dissolvingo Condensingo Freezing
What do you think is the difference between a reaction and process?
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Experiment
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Complete page 69 Questions 1-8
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Endothermic Reactions
Endothermic reactions cannot occur spontaneously. When endothermic reactions absorb energy, a temperature drop is measured during the reaction.
An endothermic reaction is one which takes heat energy from the surroundings
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Cools
HeatenergyIs used up during the reaction so the contents in tube feel cold
Starts 25°C Cools to 5°C
Ammoniumnitrate
Water
Endothermic reactions cause a decrease in temperature.
Endothermic Reactions
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Example of Endothermic Reactions
• When you squeeze the plastic bag the water reacts with the ammonium nitrate crystals, and the reaction dissolves the ionic bonds in the ammonium nitrate.
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Another example of Endothermic reactions
• An important endothermic reaction is photosynthesis.
• Plants need energy from sunlight to make glucose and oxygen from carbon dioxide and water.
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Endothermic Processes
Changes of stateFor ice to melt, the water molecules must gain energy.For water to boil and turn into steam, the water molecules must gain even more energy. These are both endothermic processes. Energy is needed to make these changes happen.
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Endothermic Examples
• Chemical Reactionso Baking breado Cooking an egg
• Physical Processeso Sometimes dissolvingo Cold packso Melting and boiling
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Complete Page 71
questions 1-5
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