Physical & Chemical Changes By Aimee Chavez

Physical Changes A physical change is a change that affects one or more physical properties of a substance. The appearance, shape, or size of a substance may be altered during a physical change. Physical changes, such as changes in state, do not change the chemical identity of a substance.

Examples of Physical Changes

Chemical Change A chemical change is the process when one or more substances change into entirely new substances with different properties. A substance’s identity changes because the chemical makeup changes. Bonds get rearranged and/or new bonds form.

Chemical Changes 1.Odor or Change in taste: (sour), Curdling of milk , browning fruit 2. Change in Color : Rusting/tarnishing, hair dye or bleach, toast, burning toast or food 3. Production of gas:(expanding /rising & bubbles), Baking a cake or bread, Making cheese 4. Hissing or Loud Noise (fire works) 5. Formation of precipitate 6. Disappearance or appearance of a new substance: frying and egg, eggs in baking a cake

Recognizing chemical changes Changing color is a clue that a new substance is formed. A bracelet turning darker such as tarnishing. 2 Ag + H2S ----> Ag2S + H2.

Corrosion & Rusting Corrosion: is the loss of metallic properties of a metal due to oxidation and the formation of unwanted products. Metals all corrode over time loosing strength, luster and electrical conductivity.

RUST Rusting is the corrosion of iron .The formation of a reddish brown flakes which loosely adheres to the iron is called rust. The overall chemical equation for the formation of rust is Iron + water → oxygen rust 4 Fe(s) + 6 H2O(l) + 3 O2(g) → 4 Fe(OH)3(s)

Change in odor or taste When an egg is rotting it is going through a chemical change and produces the smell of sulfur.

Formation of heat , light, and sound

Production of Gas Baking soda + Vinegar NaHCO3 + CH3COOH => CH3COO-Na+ + H2O + CO2 Sodium bicarbonate and vinegar => Sodium acetate and water and carbon dioxide Bicarb of soda can also neutralize both acids and bases

Yeast Yeast is one kind of fungus. Yeast can use sugar as food. Several chemical changes are occurring inside the bottle. The yeast causes the sugar to turn into alcohol, carbon dioxide, and energy. Carbon dioxide fills the balloon.

Formation of precipitate: A precipitate is a solid that forms out of solution. A common example is that of the mixing of two clear solutions: (1) silver nitrate (AgNO3) and (2) sodium chloride (NaCl): The reaction is Because lead iodide is not soluble it comes out of solution, or precipitates. It is yellow because that is just the color of the substance. Although the color can be changed by heating (to red), it will precipitate as a yellow solid every time

Curdling Milk Curdling of milk When raw milk is left standing for a while, it turns sour. This is the result of fermentation: lactic acid bacteria turning the milk sugar into lactic acid. This fermentation process is exploited in the production of various dairy products such as cheese and yogurt

Chemical Changes of Baking a Cake Baking soda is a leavening agent that causes a cake to rise by producing bubbles of carbon dioxide, as well as the byproducts of water and sodium carbonate Baking powder is baking soda that has already been neutralized with the addition of an acid . mix and a softer finished product.

Baking a Cake Eggs When eggs are cooked, the protein molecules become uncurled when exposed to heat and create new molecular bonds with other nearby protein molecules. When the egg is completely cooked, it helps form a protein network that gives the cake structure.

Soda bottle & Balloon experiment Measure 1/2 tablespoon of yeast and pour it into the soda bottle. Measure 1/2 tablespoon of sugar and pour it into the bottle. Measure 1/2 cup warm water and pour it into the bottle. Swirl the bottle so that all of the contents are well mixed. Ask an adult or a friend to hold the bottle while you put your balloon over the mouth of the bottle. Observe your bottle every five minutes.

Conservation of Mass The mass of the product is always equal to the mass of the reactants. This is known as the Law of Conservation of Mass : that mass is neither created nor destroyed in a chemical reaction.

Law of Conservation of Mass The law of conservation of mass states that in ordinary chemical and physical changes, mass is not created or destroyed. It is only transformed into different substances.

Chemical Equations Reactants  Products Carbon + Oxygen  Carbon Dioxide C + O2  CO2

Speeding up Chemical Reactions 1. Breaking a solid into smaller sizes (to increase its surface area) 2. Increase the concentration (↑ substance) 3. Increase the temperature ( more kinetic energy) 4. Decreasing volume 5. Adding a catalyst

Chemical Weathering The breakdown of rocks resulting in a change of chemical composition. 1. Oxidation : Oxygen combines with the elements in the rock and it reacts. (Rust) 2. Hydration: water can dissolve away and change the chemical composition of rocks. 3. Carbonation: Carbon dioxide dissolves in water to form carbonic acid. This makes acid rain which chemically weathers (dissolves rocks.