Mod H, U4, Les 1 Chemical Reactions Flashcards
What is a chemical reaction?
The process in which atoms are rearranged to produce new substances.
(Remember the cake example)
What are some signs that a chemical reaction has happened?
- change in color, -change in smell. -a precipitate formation
- appearance of gas and bubbles
What is a precipitate?
O
What is a chemical formula?
Uses chemical symbols and numbers to represent a given substance.
What is a subscript?
The number written below and to the right of a chemical symbol.
Example: H2O. (The 2 represents that there are 2 atoms of Hydrogen in the water. No number after the O means 1 atom)
What is a chemical equation?
Is an expression that uses symbols to show their relationship between the starting substances and the substances that are produced by the chemical reaction. Example: C + O2 yields CO2
What are reactants in a chemical formula?
Are the substances that participate in a chemical reaction. There chemical formulas are written on the left of the equation.
Example: In C + O2 yields CO2, the C + O2 are the reactants.
What is a product?
The substances forms in a reaction. Their chemical formulas are written on the right.
Example C + O2 yields CO2. The CO2 is the product.
The law of conservation of mass states?
Matter is neither created nor destroyed in ordinary physical and chemical changes.
When writing chemical equations, you must be sure that the reactants and products contain the same number of tattoos of each element. This is called…
Balancing the equation. (Think of a see saw).
What does a coefficient do?
It is written in front of a chemical formula in order to balance the equation.
Example: 3H2O means 3 molecules of water.
To find out how many atoms are in a particular molecule, one needs to multiply which two numbers together?
Multiply the subscripts of each atom by the coefficient.
Example: 2H20.
Hydrogen: 2x2= 4 hydrogen atoms
Oxygen: 1 x 2 = 4 oxygen atoms
A chemical reactions that requires an input of energy is called what?
Example?
Endothermic reaction: example- plant leaves absorb the sun’s energy to perform photosynthesis.
A chemical reaction in which energy is released is called what?
Example?
Exothermic reaction.
Example: when you burn a candle, you feel heat.
Energy cannot be created nor destroyed, but energy can change its form.What is the name of this law?
Law of Conservation of Energy.
