5.1 Exothermic and endothermic reactions 13 April 2015 What do the words endo and exo mean before a word? Exoskeletons Endoskeletons 5.1 Exothermic and endothermic reactions 13 April 2015 • Energy is involved in chemical reactions. • Energy changes in a chemical reaction can be measured. The space shuttle main engines burn hydrogen and oxygen in an exothermic reaction at 3400°C. The three engines produce the equivalent of 37 million horsepower! Exothermic reactions • Exothermic reactions give out heat to the surroundings e.g. burning, respiration How can you tell a reaction is exothermic? 25o C magnesium Gets hot Hydrochloric acid 45o C Heat energy given out Endothermic Reactions Endothermic reactions cause a decrease in temperature. Ammonium nitrate Cools Water Starts 25°C Cools to 5°C Heat energy taken in as the mixture returns back to room temp. Returns to 25°C Measuring energy changes Method 1. 2. 3. 4. Measure 25 cm3 of copper sulfate solution (HARMFUL) into the coffee cup. Measure the temperature every 30 seconds for two minutes. Add 1 g of zinc powder (FLAMMABLE) to the cup and quickly put on the lid and stir constantly. Take the temperature every 20 seconds for three more minutes. Results Draw a results table to show the temperature changes over 5 minutes. Questions 1. Plot your results as a graph. What do you notice about the temperature during the reaction? 2. Is this reaction exothermic or endothermic? How do you know? 3. How could you improve this experiment? Think about where heat may be lost. 5.1 Exothermic and endothermic reactions 13 April 2015 Most students should be able to: • State a definition for exothermic and endothermic reactions. • List one example of an exothermic and endothermic reaction. • Recognise an endothermic or exothermic reaction when data is given. • Describe how a reaction can be monitored for its energy changes. Some students should also be able to: • Explain the difference between exothermic and endothermic reactions. Quiz next Exothermic or endothermic? Hold up your card with ‘Exothermic’ or ‘Endothermic’ written on it to vote! Thermal decomposition of marble? Endothermic Combustion of methane? Exothermic Photosynthesis? Endothermic Neutralisation of an acid and an alkali? Exothermic Rusting of iron? Exothermic Thermal decomposition of copper carbonate? Endothermic Respiration? Exothermic The End!