Eyeseeyou most of your questions are dumb, but ill help u cause im in a good mood.
2. Pure substances have a constant, definite composition. Why? It cannot be separated into simpler substances by physical means. Why? - The literal dictionary definition of pure is unmixed, so a pure substance cannot be separated, because there is nothing there but that substance.
3. If there is an imbalance in chemical equation, why would we need to add extra numbers in order to balance it?- Because numbers can change around the equation so that it works. For example, the electrolysis of water. We know that Hydrogen and Oxygen are diatomic elements so they exist naturally as H2 and O2, respectively. The electrolysis would have them as H2O -> H2 + O2. However, this isnt balanced and there isnt an equal amount of oxygen on both sides. As mass can not be lost or gained, simply transformed, we must find a way to ensure both sides contain the equal amount of Hydrogens and Oxygens. So the equation becomes 2H2O -> 2H2 + O2. The numbers make it so that there is 4 hydrogen on both sides (equal) and 2 oxygen on both sides (equal).
4. Why is sodium+hydrochloric acidSodium chrloride+hydrogen gas? This reaction exists like that because the General form of a Metal + Acid reaction, is that it forms a Salt and Hydrogen Gas. In this instance, as the metal is a sodium and the acid is a chloride. Sodium chloride is formed alongside Hydrogen gas.
5. Why does delta H represent a change in heat energy (enthalpy)? In a lot of instances, Chem, Economics etc, "Delta" denotes a change. The H stands for heat, thus Delta H, means Change in Heat.
6. Why does delta H < 0 represent heat energy released (exothermic)? If Delta is less than zero, it means that energy was released in this reaction away from the reactants. Think for example, a drum of oil burning. When the oil catches fire, it releases heat energy which moves away from the fire.
7. Why does delta H>0 represent heat energy absorbed (endothermic)? Because an endothermic reaction requires energy (usually to break bonds) to be inputted into the reaction. For example, the thermal cracking of hydrocarbons (making chains into smaller chains) requires heat energy to break the bonds of the hydrocarbons.
8. Why are elements considered the simplest substances which cannot be broken down into further physical and chemical means? Because elements are pure substances. (see above)
9. Why are elements made up of only one type of atom? They just are, thats the definition of an element.
10. Why are all known elements listed on the periodic table? Because scientists devised this because its an easy way to compare and visualise trends with elements.
