Chemical Change Basics
A change that alters the form of a substance but does not create a new substance (e.g., cutting wood or melting ice).
Physical change
The substances you start with in a chemical equation.
The reactants
How many total atoms are in H2SO4?
7 atoms
A piece of paper is cut into tiny pieces. Is this a physical or chemical change?
Physical change. The paper's size and shape change, but its composition stays the same.
The name of the process used to make an equation obey the Law of Conservation of Mass.
What is balancing the equation?
The formation of a gas (bubbles) or a change in temperature are often signs of this type of change.
Chemical change (or chemical reaction)
The substances that are produced or formed at the end of a chemical reaction.
The products
How many oxygen atoms are in 3CO2?
6 oxygen atoms
A silver spoon turns black after reacting with substances in the air. Is this a physical or chemical change?
Chemical change. A new substance forms on the silver's surface.
In the unbalanced equation H2 + O2 --> H2O, the number of oxygen atoms on the reactant side is this.
What is two?
A solid that forms and separates from a liquid mixture during a chemical reaction.
A precipitate
This principle states that the total mass of the reactants must equal the total mass of the products.
Law of Conservation of Mass
How many total atoms are represented by 2Al2(SO4)3?
34 atoms
Water is heated until it boils and becomes steam. Is this a physical or chemical change?
Physical change. The water changes state, but remains H₂O.
The coefficient 2 in front of H2O means there are this many total Hydrogen atoms in the product.
What is four (4)?
A chemical reaction that releases energy, making the surroundings feel warmer, like burning wood.
Exothermic reaction
A number placed in front of a chemical formula to ensure the number of atoms for each element is equal on both sides of the arrow.
Coefficient
In the equation 2H2+O2 --> 2H2O, how many hydrogen atoms and oxygen atoms are present on each side?
4 hydrogen atoms and 2 oxygen atoms on each side
Two clear liquids are mixed, and a cloudy solid forms at the bottom of the container. What evidence indicates a chemical change?
Formation of a precipitate, indicating a new substance has formed.
The two elements involved in the single replacement reaction Al+CuO --> Al2O3 + Cu
What are Aluminum (Al) and Copper (Cu)
A chemical reaction that absorbs energy, causing the temperature of the surroundings to drop.
Endothermic reaction
If the total mass of the products is 90 grams, this was the total mass of the reactants, according to the Law of Conservation of Mass.
90 grams
A student writes Mg+O2 --> MgO. What coefficient must be placed in front of MgO to balance the oxygen atoms, and what coefficient must then be placed in front of Mg?
2 in front of MgO and 2 in front of Mg
A glow stick is snapped, causing two chemicals inside to mix and produce light. No flame or noticeable heat is produced. What type of change occurs, and what evidence supports your answer?
Chemical change. The reaction produces light as energy is released.
The type of reaction in which a fuel, like methane (CH4), combines with oxygen to produce carbon dioxide and water.
What is a combustion reaction?