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Unit 2 Review: Chemical Reactions
Terms in this set (21)
made of atoms; has mass AND volume
Changes only the physical properties of matter; the final product is still the same matter. The chemical composition (molecules) of the substance are NOT affected.
Examples of physical changes
Phase changes, cutting paper, mowing grass
The molecules of a substance are broken down and rearranged causing a change in chemical properties and, occasionally, a change in energy
Examples of chemical changes
Rusting/tarnishing; bubbles forming when alka seltzer and water are mixed; burning paper
Evidence of a chemical change
Heat, bubbles, odor, color change, sound, light, energy change, new molecules form
Law of conservation of mass
Scientific law that states: matter cannot be created or destroyed in chemical reactions.
Reactants of a chemical equation (example)
Products of a chemical equation (example)
Big idea for physical/chemical changes
To distinguish between a physical change and chemical change, an observer must make careful observations of the properties of the matter before and after the change.
Physical change because the molecules are not rearranging into something new - just spreading apart or coming together
An ice cube melting into water in your drink
example of a physical change since the ice is melting (molecules of water are simply spreading apart)
Dissolving a drink mix into water
example of a physical change since the mix/powder is just spreading out and mixing into the water
Tarnish forms on a penny
example of a chemical change since the tarnish is a change in molecules as the metals react with oxygen
Letting Jello set in the fridge
example of a physical change since the gelatin is simply changing from a liquid to a solid (phase change)
Leaves change color in the fall
example of a chemical change since the chlorophyll in the leaves is going through a chemical change
Mass before and after reaction must always be...
A reaction that ABSORBS energy in the form of heat
a chemical reaction in which heat is released to the surroundings
temperature change in endothermic reaction
temperature of the system will decrease over the course of the reaction
temperature change in exothermic reaction
temperature of the system will increase over the course of the reaction
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