Chemical Reactions Section 2 4 Chemical reactions When

Chemical Reactions Section 2. 4

Chemical reactions When chemical reactions happen bonds between atoms are formed or broken, substances change into different substances. When this happens inside organisms, it is called metabolism.

Substances that undergo chemical reactions are called reactants. Reactants are what you begin with. Substances formed are called products. Products are what you end up with.

There is a certain amount of energy required to start a reaction There is a certain amount of energy required to break a bond.

Some Reactions release more energy Some reactions absorb more energy

Writing Chemical Equations Atoms are never created nor destroyed in a reaction, so equations (formulas that represent atoms and molecules) must always be balanced.

Example C + O - CO 2 reactants products Na + Cl 2 -- Na. Cl reactants products Coefficient is the number in front of an atom or molecule. It tells how many molecules there are. It can be used to balance. The subscription tells how many atoms of an element.

What do you need to balance the equation? ___ H 2 + ____ O 2 - ___ H 2 O A. 1, 1, 1 B. 1, 2, 1 C. 2, 1, 2 D. 2, 2, 2

What do you need to balance the equation? ______Fe +_____Cl 2 -- _____ Fe. Cl 3 A. 3, 2, 3 B. 2, 3, 2 C. 2, 1, 2 D. 1, 2, 1

What do you need to balance the equation? ___Cu +___Ag. NO 3 - ___ Cu(NO 3)2 +___ Ag A. 1, 2, 1, 2 B. 2, 1, 2, 1 C. 3, 2, 1, 2 D. 2, 3, 2, 1

What do you need to balance the equation? ____Zn +___HCl - ___Zn. Cl 2 +___ H 2