4. thinking critically applying concepts
balance the following chemical equations by
adding coefficients:
a. hci + naoh + h2o + nacl
b. fe2o3 + c → fe + co2
c. so2 + o2 → so3

a. HCI + NaOH ---> H2O + NaCl

b. 2Fe2O3 + 3C → 4Fe + 3CO2

C. 2SO2 + O2 → 2SO3

the potential energy of the reactants is 200j.

from the energy diagram, the energy of the product formed is 350j; this means that, this reaction is an endothermic reaction, because it absorbs energy from its environment.

chemical changes occur when a substance combines with another to form a new substance, called chemical synthesis or, alternatively, chemical decomposition into two or more different substances. these processes are called chemical reactions and, in general, are not reversible except by further chemical reactions. some reactions produce heat and are called exothermic reactions and others may require heat to enable the reaction to occur, which are called endothermic reactions. understanding chemical changes is a major part of the science of chemistry.