What affects reaction rate
Four factors speed up most reactions: higher temperature (particles move faster and collide harder/more often), higher concentration (more particles in a given volume means more frequent collisions), greater surface area of a solid reactant (more particles exposed for collision), and a catalyst (provides an alternative reaction pathway with lower activation energy).
Example 1: Powdered calcium carbonate reacts faster with hydrochloric acid than an equal mass of marble chips. Explain why.
Powdered calcium carbonate has a much greater surface area than the same mass in chip form, exposing more particles to collide with acid particles at any moment, so the reaction proceeds faster.
Chemical equilibrium and Le Chatelier's principle
In a reversible reaction at equilibrium, both the forward and reverse reactions are still happening, just at equal rates, so overall concentrations appear constant. Le Chatelier's principle predicts that increasing a reactant's concentration, increasing pressure (for gas reactions with fewer moles on one side), or changing temperature will shift the equilibrium position to partially oppose that change.
Exothermic and endothermic reactions
Exothermic reactions release heat, so the surroundings get warmer (e.g. combustion, neutralization). Endothermic reactions absorb heat, so the surroundings get colder (e.g. dissolving ammonium nitrate in water, thermal decomposition).
Example 2: When solid ammonium nitrate is dissolved in water, the temperature of the solution drops. Classify this process and explain what "drops" tells you.
This is endothermic -- the process absorbs heat energy from its surroundings (the water and solution) to break apart the solid's structure, which is why the temperature you measure decreases.