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Transcript
Chemical Reactions Ms. Mudd 8th Grade Chemistry Chemical Reactions Objectives ► State how matter and changes in matter can be described ► Explain how you can tell a chemical reaction occurs. Chemical Reactions ► What is matter? ► Anything that has mass and takes up space ► What is chemistry? ► Study of matter and how it changes Chemical Reactions Matter has 2 major properties ► 1.) Physical property- characteristic of a substance that can be observed without changing it into another substance. ► What are some examples of physical properties? ► Temperature, Color, Texture, Flexibility ► Physical Change- any change that alters the form or appearance of a substance but doesn’t change it into another substance. Chemical Reactions ► 2.) Chemical Property- characteristic of a substance that describes its ability to change into another substance ► What are examples of chemical properties? ► Burning, Tarnishing, Rusting ► Chemical Change- A change in matter that produces one or more new substances ► Occurs when bonds break and new bonds form. Chemical Reactions Physical Change or Chemical Change? ► Ice melting? ► Physical ► Burning Magnesium causes it to combine with oxygen in the air, forming Magnesium oxide ► Chemical ► Flattening a marshmallow? ► Physical ► Roasting a marshmallow? ► Chemical ► Water left in a cup disappearing over time? ► Physical Chemical Reactions Two observable changes of chemical reactions 1. Changes in properties ► Color Change ► A solid may appear when 2 substances are mixed (Precipitate) ► A gas may form from a liquid or solid (bubbles may form) Chemical Reactions ► When water is boiled and bubbles form, is it a chemical change? ► No ► Electrolysis of water produces H2 gas and O2 gas. Is this a chemical change? ► Yes ► Color change in leaves because chlorophyll is being produced. Is this a chemical change? ► Yes Chemical Reactions 2. Changes in Energy ► What are some types of energy? ► Heat, Light, Electricity ► As matter changes, it can release or absorb energy ► This is usually observed by temperature Chemical Reactions Endothermic Reaction ► Endo= In Thermic= Heat ► Reaction in which energy is absorbed ► When frying an egg, energy is being absorbed causing the egg whites to go from a liquid to solid form Chemical Reactions Exothermic Reaction ► Exo= out Thermic= Heat ► Reaction in which energy is released (usually as heat) ► In an airplane, Fuel and oxygen react releasing energy in the form of heat ► The expansion and movement of the gases out of the plane exerts enough force to shoot the plane forward.