TOPIC 7 CHEMICAL REACTIONS. CHEMICAL CHANGES... What are some ways that you can tell that a chemical...
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Transcript of TOPIC 7 CHEMICAL REACTIONS. CHEMICAL CHANGES... What are some ways that you can tell that a chemical...
TOPIC 7CHEMICAL REACTIONS
CHEMICAL CHANGES...
•What are some ways that you can tell that a chemical reaction has occurred?
IN CHEMICAL REACTIONS…• A NEW SUBSTANCE IS FORMED
• EVIDENCE OF THE REACTION MAY INCLUDE:• COLOR CHANGE
• FORMATION OF AN ODOR
• FORMATION OF A PRECIPITATE
• FORMATION OF A GAS
• RELEASE or ABSORPTION OF HEAT/ENERGY
WHAT ABOUT THESE SCENARIOS?• Smelling a cake in the oven?• Watching ice melt?• Frying up an egg for
breakfast?• Bubbles forming when
mixing baking soda and vinegar?
BREAKING CHEMICAL BONDS
• Energy is stored in chemical bonds• To break bonds, energy must be added
•When bonds form, energy is released
• Reactants - CHEMICALS at the BEGINNING of a reaction.
• Products - NEW MATERIALS produced at the END of a reaction.
Ex.• wood + oxygen carbon dioxide + water + E• What are the + sign and for?
WRITING REACTIONS
WORD equations:
silver + bromine silver bromide
CHEMICAL equations:
Ag (s) + Br2(l ) Ag Br (s)
LAW OF CONSERVATION OF MASS
In all chemical reactions: The total mass of products is always the same as the total mass of reactants.
Reactants mass = Products mass
Matter cannot be created or destroyed.
•Closed System: nothing is allowed to enter or leave the reaction.
•Open System: matter and energy can enter or leave the reaction (so we have to account for this change).
LAW OF CONSERVATION OF MASS• Closed system:
Mg (s) + S(s) MgS(s)
24.3 g 32.1g 56.4g
• Open system:
Alka-Seltzer + Water Product
10g 100g 106 g
• ENERGY can be placed on either side of a chemical reaction depending on whether it’s being released or absorbed.
• Endothermic : energy is a reactant or “absorbed”• Exothermic : energy is a product or “released”
NAME THE REACTANTS AND PRODUCTS IN EACH EQUATION:
1. Ca + Cl2 CaCl2
2. H2O(l) H2(g) + O2(g)
3. 2Mg(s) + O2(g) 2MgO(s) + light
4. aluminum + fluorine aluminum fluoride
5. zinc + hydrogen chloride zinc chloride + hydrogen