Chemical reactions Study Guide

Chemical reactions involve breaking existing bonds between atoms and forming new ones. For bonds to break, the reactant molecules must collide with sufficient energy. This minimum amount of kinetic energy that colliding particles must possess for a reaction to occur is called the activation energy. Think of it as an energy barrier that reactants must overcome before they can transform into products. If particles collide with less energy than the activation energy, they will simply bounce off each other without reacting. Supplying activation energy can happen through various means, such as heating the reactants, which increases the kinetic energy of the particles, leading to more frequent and energetic collisions. Catalysts also play a role by providing an alternative reaction pathway with a lower activation energy, thereby speeding up the reaction without being consumed themselves. The activation energy is unique for each specific chemical reaction and is a fundamental concept in understanding reaction rates and mechanisms.

The pH scale is a measure of how acidic or alkaline a solution is. The scale runs from 0 to 14. A pH of 7 is neutral, like pure water. A pH less than 7 indicates an acidic solution, with lower numbers meaning stronger acids. A pH greater than 7 indicates an alkaline (also called basic) solution, with higher numbers meaning stronger alkalis. To accurately determine the pH of a solution, two main techniques are commonly used: pH indicators and pH meters. pH indicators are substances that change colour depending on the pH of the solution they are in. Universal indicator is a mixture of several indicators that shows a range of colours across the entire pH scale, making it useful for estimating pH values. Litmus paper is a simpler indicator, turning red in acidic solutions and blue in alkaline solutions, but it only tells you if a solution is acidic or alkaline, not the specific pH value. A pH meter, on the other hand, is an electronic device that measures the pH of a solution much more precisely. It consists of a probe, which is dipped into the solution, connected to a meter that displays the pH value digitally. pH meters are more accurate and provide a quantitative reading, unlike indicators which give a qualitative or approximate estimate.