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Chemical Reactions

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Greta Dorshorst

on 31 May 2011

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Transcript of Chemical Reactions

Observing Chemical Change Warm Up:
1.) What is one chemical reaction you know of, tell us what you know about it? 2.) Did you know that the
Statue of Liberty is actually
copper? How do you think
it got this way? Changes in matter can be described Changes in matter can be described in terms of physical and chemical changes. Chemical reactions involve changes in properties and changes in energy that you can often observe. Physical Change: is any change that alter the form or appearance of a substance but does not change it into another substance. Chemical Change: a change in matter that produces one or more substances. Reactants: substances that undergo a chemical change. Products: the new substances that form. Example: this leaf undergoes chemical changes of rot (or the reactant) and is now called a dead leaf (or product). CHANGES Exothermic Reactions: the energy released as the products form is greater than the energy required to break the bonds of the reactants. Describing Chemical Reactions Endothermic Reactions: more energy is required to break the bonds of the reactants than is released by the products. Example: heat is exothermic. + = Vinegar and Baking Soda Like the experiment about to be shown, Vinegar and Baking Soda combined makes a reaction that is Endothermic. A chemical equation tells you the substances that are formed at the end. In a chemical reaction, all of the atoms present at the start of the reaction are present at the end of the reaction. Three types of chemical reactions are synthesis, decomposition, and replacement. Chemical Equation: is a way to show a chemical reaction, using symbols instead of words. FOR EXAMPLE: You all know what this is…what’s the chemical equation? = 1 Hydrogen + 2 Oxygen = H2O = Water (YUM) Fact: the number in chemical equations is called the coefficient. Law of Conservation of Mass: states that during a chemical reaction, matter is not created or destroyed. CREATION DESTROY Open system: matter can enter from or escape to the surroundings. Can you think of anything that involves open systems? Closed system: matter does not enter or leave. Can you think of anything that involves closed systems? Raise your hand if you have one! Remember there are three types of Chemical Reactions… do you remember what those are? Synthesis
Replacement Synthesis: when two or more elements or compounds combine to make a more complex substance, the reactions is classified as synthesis. Decomposition: is a reaction that occurs when compounds break down into simpler products. Replacement: when one element replaces another element in a compound, or if two elements in different compounds trade places, the reaction is this. Controlling Chemical Reactions All chemical reactions need a certain amount of activation energy to get started. Factors that can affect rates of reactions include surface area, temperatures, concentration, and the presence of catalysts and inhibitors. Activation Energy: is the minimum amount of energy needed to start a chemical reaction. In our textbook, they give the example of a snowboarder. They won’t begin going down the mountain, until they have energy from the reactants to push them. EXPERIMENT TIME + = This experiment represents and describes how temperature can change the affects of the rate of the reactions. Catalyst: increases the reaction rate by lowering the activation energy needed. Enzymes: the cells in your body contain thousands of biological catalysts that are called enzymes, these help the reactions that occur at body temperature. Inhibitor: a material used to decrease the rate of a chemical reaction is called an inhibitor. QUIZ TIME! 1.) Which of the following results in a chemical change in matter?
a.) bending a straw
b.) boiling water
c.) braiding hair
d.) burning wood 2.) Which of the following results in a physical change in matter?
Baking soda and vinegar
Cutting an apple in half 3.) What is the number called in a chemical equation? 4.) True or False?
A principle that states during a chemical reaction, matter cannot be created or destroyed. This is called the Law of Conservation of Mass. 5.) What is one thing you learned from one of our groups experiments we did? What was your favorite one? Why? We hoped you learned something…Thanks for listening!
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