A calorimeter is used to measure the amount of heat absorbed or released during a chemical reaction.A calorimeter is used to measure the amount of heat.

Presentation on theme: "A calorimeter is used to measure the amount of heat absorbed or released during a chemical reaction.A calorimeter is used to measure the amount of heat."— Presentation transcript:

A calorimeter is used to measure the amount of heat absorbed or released during a chemical reaction.A calorimeter is used to measure the amount of heat absorbed or released during a chemical reaction. In todays experiment you will measure the heat of a reaction in a calorimeter that is made out of 2 Styrofoam coffee cups.In todays experiment you will measure the heat of a reaction in a calorimeter that is made out of 2 Styrofoam coffee cups. The inner cup holds an aqueous reaction mixture. The outer cup gives additional thermal insulation from the surrounding environment. The thermometer is used to measure the initial and final temperatures of the reaction mixture.The inner cup holds an aqueous reaction mixture. The outer cup gives additional thermal insulation from the surrounding environment. The thermometer is used to measure the initial and final temperatures of the reaction mixture. CH 104: HEATS OF REACTION

CALORIMETRY The first law of thermodynamics says that energy, in all its forms, is conserved in all processes. Or the heat lost (q lost ) by a system equals the heat gained (q gained ) by the surroundings.The first law of thermodynamics says that energy, in all its forms, is conserved in all processes. Or the heat lost (q lost ) by a system equals the heat gained (q gained ) by the surroundings. q lost + q gained = 0 The fundamental equation of calorimetry says the heat lost by a reaction (q lost = q reaction ) is gained by the surrounding water and calorimeter (q gained = q water + q calorimeter ).The fundamental equation of calorimetry says the heat lost by a reaction (q lost = q reaction ) is gained by the surrounding water and calorimeter (q gained = q water + q calorimeter ). q reaction + q water + q calorimeter = 0 q is negative ifq is negative if heat is lost. q is positive ifq is positive if heat is gained. q is measuredq is measured in joules (J).

CALORIMETRY Again, the fundamental equation of calorimetry isAgain, the fundamental equation of calorimetry is q reaction + q water + q calorimeter = 0 4.184 joules (J) are needed to heat 1 gram (g) of water 1 degree Kelvin (K). This is the specific heat of water. Therefore, the heat gained by the water is4.184 joules (J) are needed to heat 1 gram (g) of water 1 degree Kelvin (K). This is the specific heat of water. Therefore, the heat gained by the water is And the heat gained by the calorimeter isAnd the heat gained by the calorimeter is q calorimeter = (heat capacity of the calorimeter) x (T final – T initial ) Where The mass of water is in grams.The mass of water is in grams. The heat capacity of each calorimeter is unique. Therefore, in todays experiment you will measure the heat capacity of your calorimeter.The heat capacity of each calorimeter is unique. Therefore, in todays experiment you will measure the heat capacity of your calorimeter. T final is the final temperature of the water in either Kelvin or Celsius.T final is the final temperature of the water in either Kelvin or Celsius. T initial is the initial temperature of the water in either Kelvin or Celsius.T initial is the initial temperature of the water in either Kelvin or Celsius. Why can these temperatures be measured in either Kelvin or Celsius?Why can these temperatures be measured in either Kelvin or Celsius? A Kelvin degree is the same size as a Celsius degree. Therefore, the change in temperature is the same if it is measured in either Kelvin or Celsius.A Kelvin degree is the same size as a Celsius degree. Therefore, the change in temperature is the same if it is measured in either Kelvin or Celsius.

CALORIMETRY Again, the fundamental equation of calorimetry isAgain, the fundamental equation of calorimetry is q reaction + q water + q calorimeter = 0 OrOr q reaction = –(q water + q calorimeter ) Then substitutingThen substituting

MEASURING THE HEAT CAPACITY OF YOUR CALORIMETER In todays experiment you will measure the heat capacity of your calorimeter.In todays experiment you will measure the heat capacity of your calorimeter. A student puts 75.0 g water in a calorimeter. The temperature of this water and the calorimeter is 21.4° C. Then he adds 74.5 g of water at 58.0° C. The final temperature of this mixture is 37.6° C. The specific heat of water is 4.184 Jg -1 K -1.A student puts 75.0 g water in a calorimeter. The temperature of this water and the calorimeter is 21.4° C. Then he adds 74.5 g of water at 58.0° C. The final temperature of this mixture is 37.6° C. The specific heat of water is 4.184 Jg -1 K -1. How much heat was lost by the hot water?How much heat was lost by the hot water? q water = 4.184 Jg -1 K -1 x 74.5 g x (37.6° C – 58.0° C) = –6.36x10 3 J How much heat was gained by the cold water?How much heat was gained by the cold water? q water = 4.184 Jg -1 K -1 x 75.0 g x (37.6° C – 21.4° C) = 5.08x10 3 J

MEASURING THE HEAT CAPACITY OF YOUR CALORIMETER How much heat was gained by the calorimeter?How much heat was gained by the calorimeter? q lost + q gained = 0 q lost by water + q gained by water + q gained by calorimeter = 0 q gained by calorimeter = –(q lost by water + q gained by water ) q gained by calorimeter = –(–6.36x10 3 J + 5.08x10 3 J) = 1.28x10 3 J What is the heat capacity of the calorimeter?What is the heat capacity of the calorimeter? Heat Capacity of the Calorimeter = q gained by calorimeter / (T final – T initial ) = 1.28x10 3 J / (37.6° C – 21.4° C) = 78.7 JK -1 Heat capacity MUST be positive. If the calculated heat capacity of your calorimeter is negative, it is wrong.

HEAT OF REACTION For a solution, the fundamental equation of calorimetry isFor a solution, the fundamental equation of calorimetry is q reaction = –(q solution + q calorimeter ) OrOr q reaction is called the heat of reaction. If q reaction is measured at constant pressure, like in our calorimeters which are at atmospheric pressure, then q reaction is also called the change in enthalpy (ΔH).q reaction is called the heat of reaction. If q reaction is measured at constant pressure, like in our calorimeters which are at atmospheric pressure, then q reaction is also called the change in enthalpy (ΔH). The change in enthalpy per mole reaction is sometimes written as.The change in enthalpy per mole reaction is sometimes written as.

MEASURING THE HEAT OF A REACTION In todays experiment you will measure the change in enthalpy ( ) for the following reaction.In todays experiment you will measure the change in enthalpy ( ) for the following reaction. Mg (s) + 2HCl (aq) H 2(g) + MgCl 2(aq) A student puts 100. mL of 2.0 M HCl (aq) (an excess) in a calorimeter. The temperature of this aqueous solution and the calorimeter is 21.4° C. Then he adds 0.252 g of Mg (s). The final mass of this solution is 100. g. The final temperature of this solution is 31.1° C. The specific heat of this solution is 3.62 Jg -1 K -1. Assume the heat capacity of the calorimeter is 78.7 JK -1.A student puts 100. mL of 2.0 M HCl (aq) (an excess) in a calorimeter. The temperature of this aqueous solution and the calorimeter is 21.4° C. Then he adds 0.252 g of Mg (s). The final mass of this solution is 100. g. The final temperature of this solution is 31.1° C. The specific heat of this solution is 3.62 Jg -1 K -1. Assume the heat capacity of the calorimeter is 78.7 JK -1. How much heat was gained by the solution?How much heat was gained by the solution? q solution = 3.62 Jg -1 K -1 x 100. g x (31.1° C – 21.4° C) = 3.5x10 3 J

MEASURING THE HEAT OF A REACTION A student puts 100. mL of 2.0 M HCl (aq) (an excess) in a calorimeter. The temperature of this aqueous solution and the calorimeter is 21.4° C. Then he adds 0.252 g of Mg (s). The final mass of this solution is 100. g. The final temperature of this solution is 31.1° C. The specific heat of this solution is 3.62 Jg -1 K -1. Assume the heat capacity of the calorimeter is 78.7 JK -1.A student puts 100. mL of 2.0 M HCl (aq) (an excess) in a calorimeter. The temperature of this aqueous solution and the calorimeter is 21.4° C. Then he adds 0.252 g of Mg (s). The final mass of this solution is 100. g. The final temperature of this solution is 31.1° C. The specific heat of this solution is 3.62 Jg -1 K -1. Assume the heat capacity of the calorimeter is 78.7 JK -1. Mg (s) + 2HCl (aq) H 2(g) + MgCl 2(aq) How much heat was gained by the calorimeter?How much heat was gained by the calorimeter? q calorimeter = (heat capacity of the calorimeter) x (T final – T initial ) q calorimeter = 78.7 JK -1 x (31.1° C – 21.4° C) = 7.6x10 2 J

MEASURING THE HEAT OF A REACTION A student puts 100. mL of 2.0 M HCl (aq) (an excess) in a calorimeter. The temperature of this aqueous solution and the calorimeter is 21.4° C. Then he adds 0.252 g of Mg (s). The final mass of this solution is 100. g. The final temperature of this solution is 31.1° C. The specific heat of this solution is 3.62 Jg -1 K -1. Assume the heat capacity of the calorimeter is 78.7 JK -1.A student puts 100. mL of 2.0 M HCl (aq) (an excess) in a calorimeter. The temperature of this aqueous solution and the calorimeter is 21.4° C. Then he adds 0.252 g of Mg (s). The final mass of this solution is 100. g. The final temperature of this solution is 31.1° C. The specific heat of this solution is 3.62 Jg -1 K -1. Assume the heat capacity of the calorimeter is 78.7 JK -1. Mg (s) + 2HCl (aq) H 2(g) + MgCl 2(aq) How much heat was evolved by the reaction?How much heat was evolved by the reaction? q reaction = –(q solution + q calorimeter ) q reaction = –(3.5x10 3 J + 7.6x10 2 J) = –4.3x10 3 J

MEASURING THE HEAT OF A REACTION A student puts 100. mL of 2.0 M HCl (aq) (an excess) in a calorimeter. The temperature of this aqueous solution and the calorimeter is 21.4° C. Then he adds 0.252 g of Mg (s). The final mass of this solution is 100. g. The final temperature of this solution is 31.1° C. The specific heat of this solution is 3.62 Jg -1 K -1. Assume the heat capacity of the calorimeter is 78.7 JK -1.A student puts 100. mL of 2.0 M HCl (aq) (an excess) in a calorimeter. The temperature of this aqueous solution and the calorimeter is 21.4° C. Then he adds 0.252 g of Mg (s). The final mass of this solution is 100. g. The final temperature of this solution is 31.1° C. The specific heat of this solution is 3.62 Jg -1 K -1. Assume the heat capacity of the calorimeter is 78.7 JK -1. Mg (s) + 2HCl (aq) H 2(g) + MgCl 2(aq) How many moles of Mg (s) reacted? The atomic weight of Mg is 24.305 g/mole.How many moles of Mg (s) reacted? The atomic weight of Mg is 24.305 g/mole. 0.252 g of Mg /24.305 g of Mg mole -1 = 0.0104 moles of Mg

MEASURING THE HEAT OF A REACTION A student puts 100. mL of 2.0 M HCl (aq) (an excess) in a calorimeter. The temperature of this aqueous solution and the calorimeter is 21.4° C. Then he adds 0.252 g of Mg (s). The final mass of this solution is 100. g. The final temperature of this solution is 31.1° C. The specific heat of this solution is 3.62 Jg -1 K -1. Assume the heat capacity of the calorimeter is 78.7 JK -1.A student puts 100. mL of 2.0 M HCl (aq) (an excess) in a calorimeter. The temperature of this aqueous solution and the calorimeter is 21.4° C. Then he adds 0.252 g of Mg (s). The final mass of this solution is 100. g. The final temperature of this solution is 31.1° C. The specific heat of this solution is 3.62 Jg -1 K -1. Assume the heat capacity of the calorimeter is 78.7 JK -1. Mg (s) + 2HCl (aq) H 2(g) + MgCl 2(aq) What is the heat of reaction in kJ/mole?What is the heat of reaction in kJ/mole?