Pamela wants to learn more about the career preferences of students in her school. she interviews a number of students from the advanced science classes. why is this sample likely to be biased? advanced science students may not have clear career preferences. the numbers of boys and girls in the advanced science classes are not equal. advanced science students are not representative of all the students in the school. it is too early for students to have career preferences while still in school. nextreset

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.