Atoms & Elements
What is the smallest unit of an element?
an Atom
What do we call a substance made of only one type of atom?
An Element
Is ice melting a physical change or a chemical change?
Physical change.
What law states that matter cannot be created or destroyed during a chemical reaction
Law of Conservation of Mass.
What type of reaction transfers energy into the surroundings?
Exothermic.
Which particle in an atom has a negative charge?
Electron
What do we call a substance made of two or more different elements chemically bonded together?
A compound.
What do we call the starting substances in a chemical reaction?
Reactants.
If you start with 10 grams of reactants in a closed system, what is the total mass after the reaction?
10 grams.
What type of process absorbs thermal energy from its surroundings?
Endothermic.
What does an element's atomic number tell us?
Number of protons
How many hydrogen atoms are in one molecule of H₂O?
2 hydrogen atoms.
Name two possible signs that a chemical reaction has occurred.
Any two: color change, temperature change, gas formation, light production, or formation of a new solid.
If 15 grams of one substance react with 10 grams of another in a closed system, what is the total mass of the products?
25 grams.
A chemical reaction makes the surrounding water warmer. Is it exothermic or endothermic?
Exothermic.
Where are protons and neutrons located inside an atom?
in the nucleus
How many total atoms are in one molecule of CO₂?
3 atoms (1 carbon and 2 oxygen).
What do we call the new substances formed during a chemical reaction?
Products.
A reaction starts with 40 grams of reactants. One product has a mass of 25 grams. What is the mass of the other product?
15 grams.
A cold pack absorbs thermal energy from your hand. Which direction does the energy move?
From your hand (surroundings) into the cold pack (system).
An atom has 8 protons, 8 neutrons, and 8 electrons. What is its atomic number, and how many total particles does it have?
Atomic number = 8; Total particles = 24.
How many total atoms are in 3 molecules of H₂O?
9 atoms (6 hydrogen and 3 oxygen).
A substance changes color and produces bubbles when mixed with another substance. Why might this indicate a chemical reaction?
The color change and gas formation may indicate that new substances have formed.
In a closed system, 12 grams of substance A react with an unknown mass of substance B to make 30 grams of products. How many grams of substance B reacted?
18 grams.
Why doesn't a temperature change always prove that a chemical reaction happened?
Because physical changes can also transfer thermal energy without producing a new substance.