chemical reactions

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Chemical Changes

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You have really changed since the fire ! CHEMICAL CHANGE

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Chemical Warming up! Name the change Physical

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Physical Physical Chemical Warming up! Name the change

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ACTIVITY

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Demonstration based worksheet What do you observe when magnesium ribbon is brought near the flame? ____________________________________________________ a) What observation tell us that addition of dilute acid to zinc granules leads to a chemical change? _________________________________________________ b) Did you feel any change in the temperature on touching the bottom of the test tube? Suggest whether the heat is being released or absorbed during the process? __________________________________________________ 3. What happens when lead nitrate solution is added to potassium iodide solution? __________________________________________________ 4. What are the indicators of a chemical change? __________________________________________________ __________________________________________________

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Temperature change Evolution of a gas Indicators of chemical change Color change Change of state

Chemical Change:

8 Chemical Change Substances are made of atoms. During chemical change, atoms in the substances are rearranged to form one or more different substances Old bonds are broken; new bonds form

Chemical Change:

Energy is needed to break bonds Energy is released when bonds are formed . Chemical reactions are accompanied by a change in energy, mainly in the form of heat . Chemical Change

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If energy is absorbed during a chemical change, the reaction is endothermic . Endothermic reaction

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If energy is released during a chemical change , the reaction is exothermic . Exothermic reaction

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Endothermic and exothermic reactions A reaction in which heat is given out is exothermic. A reaction in which heat is taken in is endothermic.

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13 Photosynthesis vs. respiration Endothermic Exothermic

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What are the characteristics of a chemical change? Differentiate between exothermic and endothermic reaction. Give an example of a chemical change accompanied by- a) Change of temperature b) Change of state c) Evolution of gas d) Change of colour LEARNING CHECK

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