Particles of Matter and Substances
What is a compound?
A substance made of two or more different atoms chemically bonded in a fixed ratio
Two molecules have the same atoms but different shapes. Why do they behave differently?
Different atomic arrangement changes properties
Sugar dissolves in water. Is it a chemical or physical change?
Chemical change
What are the substances present before a chemical reaction begins?
Reactants
What type of energy transformation occurs when chemical bonds are broken or formed?
Thermal energy
A pure substance can be made of either atoms or molecules. What makes it “pure”?
It has consistent matter and properties throughout
A substance breaks predictably along lines. What does this tell you about its structure?
It has a repeating extended structure
Milk spoils and silver tarnishes. What type of change occurs?
Chemical change
What are the substances formed during a chemical reaction?
Products
In which direction does heat always flow?
From warmer objects to colder objects
Two substances have identical appearances. One reacts with water; the other does not. What determines this difference?
Chemical properties based on atomic arrangement
A model shows atoms in a repeating pattern; another shows a small cluster. How does each explain properties?
Repeating pattern predicts rigidity; cluster predicts unique molecular properties
Water freezes and melts. Why is this a physical change?
The identity of H₂O stays the same
What must a chemical equation have to be considered balanced?
Same number of each atom on both sides
What affects how quickly a chemical reaction releases energy?
Reaction rate
Two substances contain the same atoms but are arranged differently. One is a crystal; the other is a molecule. Which will be rigid?
The crystal (extended structure)
Changing only the connections between atoms changes a substance. What does this show?
Atomic arrangement determines properties
Two nails look the same. One rusts, one does not. How can you identify the difference?
Chemical properties reveal they are different substances
What shows the types and numbers of atoms in a substance?
Chemical formula
Name the three ways thermal energy can be transferred.
Conduction, convection, radiation
Sodium and chlorine combine to form a molecule with new properties. Why is this a new substance?
The atoms are bonded differently, creating a unique particle
Sodium chloride forms a crystal, but sugar does not. Why?
The pattern of atomic connections differs
A reaction produces gas and energy, but the original substances are still visible. How do you know a chemical reaction occurred?
Atoms rearranged to form new substances
Law of conservation of matter states
Matter cannot be created or destroyed in ordinary chemical or physical changes
Name the factors that can increase the rate of a chemical reaction.
Temperature, concentration, surface area, and catalysts