Endothermic and exothermic intro labStudent:

You will perform two short laboratory activities, one reaction will see the temperature of the surroundings increase and one will see the temperature of the surroundings decrease.

Introduction

Energy can either be released or absorbed in chemical reactions. To make a chemical bond, another bond must be broken. It is the sum of the energy changes in breaking and then making the bonds that results in the total energy change, or enthalpy of the reaction ()

Materials and equipment:

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100 cm3 measuring cylinder x 2

calorimeters x 2

temperature probe

data logging software

stirring rod

20 cm3 of 3.0 mol dm-3 sodium hydroxide

20 cm cm3 of 3.0 mol dm-3sulfuric acid

40 cm3 of 3.0 mol dm-3 citric acid

12.00g sodium hydrogen carbonate solid

paper boat

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Approaches to Learning – Thinking

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Reaction 1:

  1. Pour 20 cm3 of 3.0 mol dm-3sodium hydroxide into the calorimeter.
  2. Measure the temperature for 30 seconds.
  3. Add 20 cm cm3 of 3.0 mol dm-3sulfuric acid into the calorimeter.
  4. Continue measuring until you have seen the temperature decreasing for 60 seconds.

Results

Sketch a rough graph of the data.

(Sketch- Represent by means of a graph showing a line and labelled but unscaled axes but with important features (for example, intercept) clearly indicated.)

Analysis:

  1. State the formula for the reaction.
  1. Determine the limiting reagent.
  1. Calculate the temperature change.
  1. Calculate the enthalpy of neutralization.
  1. Classify the reaction as endothermic or exothermic

Reaction 2:

  1. Pour 40 cm3 of 3.0 mol dm-3citric acid into the calorimeter.
  2. Measure the temperature for 30 seconds.
  3. Add 12.00 g of sodium hydrogen carbonate into the calorimeter.
  4. Continue measuring until you have seen the temperature increasing for 60 seconds.

Results

Sketch a rough graph of the data.

Analysis:

  1. Write the formula for the reaction.

H3C6H5O7(aq.) + 3NaHCO3(s) 3CO2(g) + 3H2O(l) + Na3C6H5O7 (aq.)

  1. Determine the limiting reagent.
  1. Calculate the temperature change.
  1. Calculate the enthalpy of reaction
  1. Classify the reaction as endothermic or exothermic.

Discussion activities

  1. List some assumptions that are made when calculating the enthalpy of the reaction.
  2. Explain the effect these assumptions could have on the results. (Would they increase or decrease the value?)
  3. Describe some sources of error in this investigation.
  4. Describe some ways of reducing sources of error in this investigation.
  5. Describe some ways of increasing the precision of this investigation.

Approaches to Teaching –Inquiry /Conceptual understanding

Approaches to Learning – Thinking

Learner profile–Knowledgeable / Inquirer /Open-minded / Thinkers