Chemical Reactions and physical changes
Which of these is a physical reaction?
1. A crumpled piece of paper
2. A hard-boiled egg
3. A burning piece of wood
1. A crumpled piece of paper
True or false:
Energy is needed for chemical bonds to break during chemical changes?
True
Most chemical reactions can be described as either...
exothermic or endothermic
Scientists represent chemical reactions with
Chemical equations
What is a coeficient
A constant term related to the properties of a product
What is the difference between a chemical change and a chemical reaction?
There is no difference
All substances are made up of molecules, which are collections of atoms.
Chemical Bonds
What is an example of an exothermic reaction
Exploding fireworks
An element with a 3 subscript is
H3
What are subscripts?
Used to show how many atoms are inside a molecule.
If a plant dies is it a physical or a chemical change?
Chemical change
What is needed to break and form chemical bonds?
Energy
True or False - Exothermic reactions release excess energy in the form of light, heat, or even chemical?
False
If an equation is not balanced, you can balance it by.....
Changing coefficients on either side.
When a molecule has both a coefficient and a subscript.....
You multiply the subscript by the coefficient to determine the number of atoms.
True or false - Is a leaf that changes color a physical or a chemical change?
Chemical change
The bonds between atoms in the reactants are broken, and the atoms of the different substances rearrange with each other to form new substances, or products.
Chemical Reaction
True or False - Endothermic reactions require more energy than they produce, which can leave the containers these reactions occur in feeling cold.
True
Has an equal number of each element’s atoms on the reactant side and the product side.
A balanced chemical equation
Scientists have created a special way to demonstrate this law in chemical equations:
coefficients and subscripts.
Which of these comes first in the transformation of a chemical reaction?
A- Atoms rearrange themselves by breaking themselves down into smaller parts
B- The atoms transform themselves
C- The atom's chemical bonds break
D- The chemical bonds of the atom bond with new elements
C
Which of these is the defintion of a chemical bond?
A- When the molecules in an atom connect through their electrons.
B- When the molecules in an atom bind with other atoms to create bonds.
C- When electrons form and bind within individual atoms.
A
True or False:
Endothermic reactions require ____ energy than/as they produce
A- Less
B- Just as much
C- More
C
What equation is it if you see 2Fe2O3
chemical equation
If you see 3H2O, you know ........
There are six hydrogen atoms (3 × 2) and three oxygen atoms (3 × 1).