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When substances react and bubbles or a vapor appears, this is an indication that a chemical reaction is occurring. Change in ColorĪ change in color is a possible indication of a chemical reaction. But it is a strong argument that one has occurred. Because many physical changes also involve heat or light, this is not concrete, definitive evidence of a reaction. One example of this is a fire or spark, which is evidence of combustion. If a reaction emits heat or light, that is an indication that energy has been released from the reaction. So how can we tell if a chemical change has occurred? 1. Indications of a Chemical Reactionīased on its definition, a chemical reaction occurs when a substance undergoes a chemical change. While some physical changes are easily reversible, such as re-freezing melted ice, reversing a chemical change requires another chemical reaction. This process changes the chemical composition of the original substance. When an iron nail comes into contact with water and is then exposed to the air, it rusts, forming a brown-red substance. Once melted or boiled, the water may be in a different form (solid ice or gaseous water vapor), but it is still water, H 2O, and it still has the same chemical composition.Ī chemical change happens when a substance’s chemical identity changes. For example, freezing or boiling water is a physical change. In a physical change, a compound’s shape may change, but its chemical identity will not. Let’s looks at some chemical change examples, and chemical reaction examples. Chemical equations express chemical reactions in terms of symbols and chemical formulas of the compounds involved in reactions. the water is able to change its form but the chemical composition remains the same and the action is reversible.So what is a chemical reaction? What is a chemical change, and what is a physical change? A chemical reaction occurs when compounds or substances undergo a chemical change to form different compounds or substances. The change of water from a liquid to a solid due to the change in temperature is classed as a physical change. When the water has become a liquid again place the cup into the freezer and allow to freeze - periodically observe the freezing

Place cup in direct sunlight and observe the melting process.ģ. Place a few ice cubes into the plastic cup.Ģ. Observe as water changes from solid to a liquid from and back againġ.

Gasses need a lot of room and the carbon dioxide starts to fill the bottle, and keeps filling the bottle until the bottle can no longer take the pressure – that’s when the explosion occurs. Quickly shake bottle then throw away from people as far as possible – observe the explosion!īy mixing vinegar (acid) and baking soda (base) an ACID-BASE reaction occurs and the two chemicals work together to create a gas (carbon dioxide). Gently push the paper towel into the bottle and quickly replace the bottle cap.ĥ. Roll up paper towelling so the baking soda will not fall out.Ĥ. Spread two table spoons of baking soda over a piece of paper towel.ģ. Half fill the plastic bottle with vinegar.Ģ. Addition of another drop of soap may start the process again.Įxperience how extreme chemical reactions can beġ. As the soap becomes evenly mixed with the milk, the action slows down and eventually stops.Īs the soap becomes evenly mixed with the milk, the action slows down and eventually stops. The chemical reaction began with the drop of soap! The soap disrupts the surface tension of the milk by dissolving the fat molecules found in the milk – causing the food colouring to move with the surface which streams away from the soap. That is because food colouring is less dense than milk, so it floats on the surface, and the colours do not mix unless you manually stir the mixture. When the food colouring was placed on the surface of the milk, nothing really happened. What would happen if you add another drop of soap after the colours have stopped moving?

Does the movement go on forever? What happens? What direction does the food colour move after the experiment has been running for a while? In which directions does the food colouring move when the soap is first added? What happens when the soap has been added? What happens to the food colouring when it is first added to the milk? Using the dropper, place one drop of dish soap onto the surface of the milk in the centre of the dish - Prepare to observe Carefully place one small drop of each of the food colours on the surface of the milk – evenly spaced.ģ. Pour a layer of milk (1 cm deep) into the dish.Ģ.