### Introduction

Some chemical reactions absorb energy and are called endothermic reactions. Many chemical reactions give off energy. Chemical reactions that release energy are called exothermic reactions. You will study one endothermic reaction and one exothermic reaction in this experiment.

In Part I, you will study the reaction between citric acid solution and baking soda. An equation for the reaction is

${{\text{H}}_{\text{3}}}{{\text{C}}_{\text{6}}}{{\text{H}}_{\text{5}}}{{\text{O}}_{\text{7}}}{\text{(aq) + 3 NaHC}}{{\text{O}}_{\text{3}}}{\text{(s)}} \to {\text{3 C}}{{\text{O}}_{\text{2}}}{\text{(g) + 3 }}{{\text{H}}_{\text{2}}}{\text{O(l) + N}}{{\text{a}}_{\text{3}}}{{\text{C}}_{\text{6}}}{{\text{H}}_{\text{5}}}{{\text{O}}_{\text{7}}}{\text{(aq)}}$

In Part II, you will study the reaction between magnesium metal and hydrochloric acid. An equation for this reaction is

${\text{Mg(s) + 2 HCl(aq)}} \to {{\text{H}}_{\text{2}}}{\text{(g) + MgC}}{{\text{l}}_{\text{2}}}{\text{(aq)}}$

### Objectives

In this experiment, you will

• Observe two chemical reactions.
• Measure temperature changes.
• Determine the change in temperature, Δt, for each of the reactions.
• Identify endothermic and exothermic reactions.