How do you find heat of formation of a solution?

Question

Jeremiah Adams · Accepted Answer

As long as the reaction is conducted in a calorimeter or other similar apparatus, such as a coffee cup calorimeter, the enthalpy change for an aqueous solution can be determined experimentally. A thermometer can be used to measure the temperature change of the solution along with the mass of the solute.

Step 1: Using a balance, determine the mass of the solute in grams. Since I'm dissolving sodium hydroxide, I've measured 4 g, or 0.1 moles.

Step 2: Measure the volume of water (I'll use 100 ml). Step 3: Record the density of the water. Using the density and volume of water, I can use the following formula to get the mass of the water:

Mass is equal to Volume x Density; if we assume that water has a density of 1 g/ml, then 100 g makes up 100 ml of water.

Step 3: Transfer 100 milliliters of water into a coffee cup calorimeter and note its initial temperature of 27 degrees Celsius.

Step 4. Add 4 g of Sodium Hydroxide to the water. Dissolve the sodium Hydroxide using a stirrer and also record the temperature of solution. Let us assume that the final temperature of the solution is #48^o# C

Step 5. In this dissolution experiment Sodium hydroxide dissolves in water and gives off heat energy to the surrounding water , which causes the temperature of water to go up from #27^o# C to #48^o# C. The change in temperature is #48^o# C - #27^o# C = #21^o# C

Step 6: To determine the amount of heat that water has gained, use the formula Q = mass of water. specific heat of water. change in temperature.

Step 7 Q = 100 g . 4.18 J / #g^oC#. #21^o# C

8.778 kJ or 8778 J is Q.

Either the salt has lost 8.778 kJ of heat energy to the water, or the water has gained 8.778 kJ of heat energy from the salt; therefore, the energy lost by the salt is -8.778 kJ.

Change in enthalpy = Q lost by salt / # of moles of salt

= -87.88 kJ/mol / -8.778 kJ / 0.1 mol

Serenity Allen · Answer

undefined The heat of formation of a solution is determined by calculating the difference in enthalpy between the final solution and the individual components in their standard states. This can be expressed as ΔH_solution = ΣnΔH_f(products) - ΣmΔH_f(reactants), where n and m are the coefficients in the balanced chemical equation for the solution formation. The standard enthalpies of formation (ΔH_f) for the substances involved are obtained from reference tables.