There are some basic rules to follow to decide when to use a capital letter and when to leave the first letter lowercase. Actually, maybe I should state that many rules in English capitalization, do not apply in Spanish. In Spanish you do not capitalize the names of the days of the week, or the months of the year.
Equations and Expressions are closely related. The primary difference between the two is an equals sign. An equation has a left side, a right side and an equals sign separating the sides. An expression, by contrast, doesn't have any sides and is simply what the name suggests: An algebraic expression.. Though sometimes it is possible to combine like terms, we are generally not expected to do or solve anything regarding expressions.
You've worked with equations in mathematics where an equation is used to represent information such as equalities or inequalities. Chemical equations are different from mathematical equations because the two parts of a chemical reaction represent the 'before' and 'after' of a chemical reaction. In mathematical equations, an equals sign separates the two parts of the equation. In chemical equations, equal signs are not used. Instead, an arrow is used to separate the two sides of the equation, and it points in the direction that a chemical reaction will proceed.