Chemical Change

Question 1

What is a chemical reaction?

Answer 1

a process that occurs when a substance/substances react to form a different substance

Question 2

what are reactants?

Answer 2

starting substances in a chemical reaction

Question 3

what are products?

Answer 3

new substances that are produced from the reaction

Question 4

what are characteristics of chemical reactions?

Answer 4

-involve the flow of energy
-consistent with the law of conservation mass
-same change of state observed
-involve the production of new substances

Question 5

What is an Exothermic reaction?

Answer 5

a reaction that releases energy usually in the form of heat, light, or electricity

Question 6

What is an Endothermic reaction?

Answer 6

a reaction that absorbs energy

Question 7

What is an example of a biochemical exothermic reaction?

Answer 7

cellular respiration, occurs in all living things

Question 8

What is an example of a biochemical endothermic reaction?

Answer 8

photosynthesis, occurs in plants

Question 9

What is the law of conservation of mass?

Answer 9

the total mass of reactants equals the total mass of products

Question 10

What is the process of writing a chemical word equation?

Answer 10

-determine the reactants & products
-set up with + and —>
Ex: magnesium + hydrochloric acid (reactants) —> magnesium chloride + hydrogen gas (products)

Question 11

What is the process of writing a chemical formula equation?

Answer 11

(skeleton equations)
-show which substances are involved but do not show the proportions
Ex: H2(g) + O2(g) —> H2O(l)

Question 12

What is the process of balancing equations?

Answer 12

-the # of atoms on the reactants side must equal the # of atoms on the product side
-use coefficients to balance. DO NOT change the subscripts
Ex: 2H2(g) + O2(g) —> 2H20(l)

Question 13

In what situation would you change H2O to HOH?

Answer 13

if hydroxide is on one side and water on the other

Question 14

True or False: coefficients apply to all elements in the formula

Answer 14

True!

Question 15

In combustion reactions, balance _ and _ before the oxygens

Answer 15

carbons and hydrogens

Question 16

True or False: you divide the subscripts by the coefficients

Answer 16

False! You multiply the subscripts by the coefficients

Question 17

Explain the process of formation (synthesis)

Answer 17

simple elements or compounds combine to form larger, move complex compounds
Ex: 2H2(g) + O2(g) —> 2H2O(l)

Question 18

Explain the process of decomposition

Answer 18

products are simpler than reactants
Ex: CaCO3–> CaO(s)+CO2(g)

Question 19

Explain the process of hydrocarbon combustion

Answer 19

products are always carbon dioxide & water
Ex: CH4 + O2 —> CO2 + H2O

Question 20

What is the rule for single replacement?

Answer 20

Cations can only switch with cations, anions can only switch with anions
Ex:
a) K + NaCl —> KCl + Na
b) Cl2 + 2NaBr —> 2NaCl + Br

Question 21

what is the rule for double replacement?

Answer 21

exchange of similar charged ions
Ex: Pb(NO3)2 + 2 KI —> PbI2 + 2KNO3