CHEMISTRY

CHEMISTRY – the science of dealing with what substances are made of and how they interact

Scientists learned about substances by analyzing them for: PHYSICAL PROPERTIES: - You can detect these without changing the substance. densitycolor

Scientists learned about substances by analyzing them for: CHEMICAL PROPERTIES: - These are characteristics seen during or after it changes in a chemical reaction Baking soda + vinegarCorn starch + water

Try to identify the following characteristics as PHYSICAL or CHEMICAL properties. #1 – Water boils at 100 degrees C PHYSICAL?CHEMICAL?

#2 – Diamonds cannot be scratched easily PHYSICAL?CHEMICAL?

#3 – Salt dissolves in water PHYSICAL?CHEMICAL?

#4 – Diet Coke & Mentos = BOOM PHYSICAL?CHEMICAL?

#5 – Yeast acts on sugar to make CO2 and ethanol PHYSICAL?CHEMICAL?

#6 – Wood is very flammable PHYSICAL?CHEMICAL?

#7 – Pumice floats in water PHYSICAL?CHEMICAL?

#8 – Mercury is a metal that is a liquid at room temperature PHYSICAL?CHEMICAL?

#9 – Dry ice can sublime at room temperature PHYSICAL?CHEMICAL?

#10 – Iron rusts in the presence of oxygen and water PHYSICAL?CHEMICAL?

CHEMICAL REACTION DETAILS

As you learned earlier, there are several additional characteristics that can make chemical reactions interesting

You just saw a reaction that gives off a large amount of heat – these are called exothermic reactions

In these reactions, less energy is needed to break old bonds than to make new ones. This results in energy being given off when the reaction proceeds.

Some reactions literally suck up heat from the environment around them – they require energy to start. These are endothermic reactions

There are times when reactions are proceeding from reactants to products, but they take a long time. To speed them up, you add a catalyst.

Example: A car’s catalytic converter

There are times when reactions are proceeding from reactants to products, but they go too quickly. To slow them down, add an inhibitor. Example: Preservatives

Law of Conservation of Mass: Particles of matter are not created or destroyed as the result of physical or chemical changes