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Calorimetry & Heat Flow - Worked Chemistry Problems

Sample Problem #1 - Coffee Cup Calorimetry

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It's called coffee cup calorimetry because a styrofoam coffee cup is used.

It's called coffee cup calorimetry because a styrofoam coffee cup makes a perfect easy-to-find container for the reaction.

Rusty Hill, Getty Images
Review

While working these problems, you may wish to review the section on coffee cup and bomb calorimetry and the laws of thermochemistry.

Problem

The following acid-base reaction is performed in a coffee cup calorimeter:

H+(aq) + OH-(aq) → H2O(l)

The temperature of 110 g of water rises from 25.0°C to 26.2°C when 0.10 mol of H+ is reacted with 0.10 mol of OH-.

 

  • Calculate qwater
  • Calculate ΔH for the reaction
  • Calculate ΔH if 1.00 mol OH- reacts with 1.00 mol H+

Solution

 

  • Use this equation:

    q = (specific heat) x m x Δt

    where q is heat flow, m is mass in grams, and Δt is the temperature change. Plugging in the values given in the problem:

    qwater = 4.18 (J / g·°C;) x 110 g x (26.6°C - 25.0°C)

    qwater = 550 J

     

  • ΔH = -(qwater) = - 550 J
  • We know that when 0.010 mol of H+ or OH- reacts, ΔH is - 550 J:

    0.010 mol H+ ~ -550 J

    Therefore, for 1.00 mol of H+ (or OH-):

    ΔH = 1.00 mol H+ x (-550 J / 0.010 mol H+)

    ΔH = -5.5 x 104 J

    ΔH = -55 kJ

Answer

 

  • 550 J (be sure to have 2 significant figures)
  • -550 J
  • -55 kJ

Would you like an example for bomb calorimetry? Then continue on to the second worked calorimetry problem > Next Page

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