Balancing Equations
The small number in a formula that shows how many atoms of an element are in a molecule.
Subscript
Why does an ice pack feel cold after being activated?
An endothermic reaction absorbs heat from your skin.
Burning paper is an example of this type of change.
Chemical
Define an exothermic reaction
A reaction that releases heat energy.
What layer of the Earth do we live on?
The Crust
The new substances are formed after a reaction.
The Products
When gasoline burns, which type of chemical reaction is occurring?
Combustion.
The rearrangement of atoms without creating or destroying them.
Chemical Reaction
Define an endothermic reaction.
A reaction that absorbs heat energy.
What are the two main gases found in the air we breathe?
Nitrogen and oxygen
2H₂ + O₂ → 2H₂O, how many hydrogen atoms are on each side?
4
In a closed system, the mass of reactants equals 24 g. What must the total mass of products be?
24g
What law states that mass is neither created nor destroyed in a chemical reaction?
Law of Conservation of Mass
The temperature of the surroundings increases during a reaction. What does this indicate?
It’s exothermic.
What scientist proposed the three laws of motion?
Isaac Newton
A number that shows how many molecules or atoms are involved in a chemical equation.
coefficient
Why must chemical equations be balanced?
To show that matter is conserved; atoms are neither created nor destroyed.
Explain why photosynthesis and cellular respiration are opposite chemical processes.
Photosynthesis stores energy (endothermic) using CO₂ and H₂O to make glucose; respiration releases energy (exothermic) by breaking glucose down.
Why do some reactions feel cold to the touch?
They absorb energy from the surroundings (endothermic).
What scale is used to measure the strength of earthquakes?
Richter scale
C₃H₈ + 5O₂ → 3CO₂ + 4H₂O
10 Oxygen
What is a pure substance made of only one kind of atom?
An element.
Rust forming on iron is what type of reaction?
Oxidation (Chemical Change).
A reaction absorbs 250 kJ of energy. Describe what happens to the bonds during this reaction.
Energy is absorbed to break chemical bonds in the reactants.
What part of the human eye controls the amount of light entering it?
The iris