Calorimetry is the measurement of heat transfer. Devices that measure the amount

Question

Calorimetry is the measurement of heat transfer. Devices that measure the amount of heat released or absorbed during a process are called calorimeters. A coffee cup calorimeter is the simplest calorimeter and is often used to measure the heats of chemical reactions at constant pressure (also called enthalpies). This calorimeter consists of a Styrofoam cup with a plastic lid and a thermometer. In today's workshop, we will use calorimetry to calculate the standard molar enthalpy of reaction or the enthalpy change that occurs in a system when 1 mole of matter is transformed by a chemical reaction at 1 atm: delta H = q_rxn (in J/mol, at constant P and pV-work only), where q = cm delta T Let's consider the following chemical experiment: A student wants to measure the heat of neutralization reaction. To do this she mixed in a coffer cup calorimeter 35.0 mL of 0.70 M HCl solution and 65.0 mL of 0.50 M NaOH solution both at 22.0 degree C initially. She then continued to measure the temperature of the mixture for 10 minutes. Write a chemical equation, a complete ionic and a net ionic equations for this reaction. Chemical equation: _________________________ Complete ionic equation: _______________________ Net ionic equation: ____________________________ Now discuss with your group the following questions: (a) what is(are) the product(s) of this reaction? (b) What is the system in this experiment and what are the surroundings? (c) Is this system an open one, a closed one or an isolated one? Before you write down your answers make sure that EVERYONE in your group can justify each them. Now write your answers below and don't forget to explain them. (a) _______________ is(are) the product(s) in this reaction. (b) The system: The surroundings: (c) We can consider this system to be an _____________ system, because:

Explanation / Answer

Q1.

chemical equation --> HCl(aq) + NaOH(aq) --< H2O(l) + NaCl(aq)

complete ionic equation --> must have all ions in solution:

HCl(aq) + NaOH(aq) --< H2O(l) + NaCl(aq)

H+(aq) + Cl-(aq) + Na+(aq) + OH-(aq) -- H2O(l) + Na+(aq) + Cl-(aq)

net ionic equation --> must get rid of spectator ions

H+(aq) + Cl-(aq) + Na+(aq) + OH-(aq) -- H2O(l) + Na+(aq) + Cl-(aq)

so:

H+(aq) + OH-(aq) -- H2O(l)

Q2.

the product of this reaction --> salt (sodium chloride) and water

b)

system --> the reaction i.e. water + NaOH + HCl solution before/after reaction

surroundings --> the calorimeteer and anything outside it

C)

we consider it a closed system, since it can't exchange mass to the outside but it CAN exchange heat to it

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