KS3 Science Home learning Reactions 2 Name: _____________________________ Class: _____________________________ Teacher: ___________________________ In this topic you will learn about: • Exothermic and Endothermic reactions. • How to represent energy changes in reactions. • How to speed up reactions. Practical skills: • Measuring temperature changes This will prepare you for: • GCSE Chemistry • GCSE Physics Maths in science: • Reading a graph • Calculating differences in temperature and energy Lesson 1: Exothermic Reactions Lesson 1: Exothermic Reactions In and On: Look at the images on the board. Are the following physical or chemical changes? 1. Ice melting 2. Frying an egg 3. Burning magnesium Challenge: What is the difference between a physical and chemical change? Learning Objectives • Describe examples of exothermic reactions • Explain the energy changes taking place during an exothermic reaction What does ‘exothermic’ mean? ____________________________________________________Exothermic reactions are reactions or processes that release energy, usually in the form of heat or ____________________________________________________light. In an exothermic reaction, energy is released ____________________________________________________because the total energy of the products is less than the total energy of the reactants. Exothermic reactions Energy changes occur in all ___________ ____________. In exothermic reactions, energy is ________ _____ , usually in the form of ______. This means that the temperature of the surroundings __________. Challenge: An example of an exothermic reaction is…. Investigating exothermic reactions Citric Acid and Baking soda Magnesium ribbon and Hydrochloric 1. Add 2cm depth of citric acid to a acid test tube 1. Add 2cm depth of Hydrochloric 2. Record temperature acid to a test tube. 3. Add 1 spatula scoop of baking 2. Record temperature soda 3. Add a few pieces od magnesium 4. Record temperature ribbon 4. Record temperature Record your observations to identify the exothermic reaction Citric acid and baking soda Magnesium ribbon and Hydrochloric acid Temperature at start (oC) 23 22 Temperature at end (oC) 10 42 Conclusion: _____________________________________________________Citric acid and baking soda is an endothermic reaction as _____________________________________________________the temperature decreases. _____________________________________________________Magnesium and hydrochloric acid is exothermic as the temperature increases. Explain, using ideas about particles and atoms, why burning magnesium is an exothermic reaction. ______________________________________________________ Burning magnesium is an exothermic reaction because ______________________________________________________ ______________________________________________________when magnesium and oxygen particles collide to form new ______________________________________________________bonds, energy is released into the surroundings. How canThis you tellreaction that this isreaction exothermic is exothermic?because the energy of the ____________________________________products is less than the energy ____________________________________ ____________________________________of the reactants 11 the temperature increases allow gets hotter / heat / energy is given off (energy of) products lower than (energy of) reactants Lesson 2 : Endothermic reactions In and On: Using only addition, how can you add eight 8's to get the number 1,000? 888 +88 +8 +8 +8 =1,000 Learning Outcomes: • Describe examples of endothermic reactions • Explain the energy changes taking place during an endothermic reaction What is the difference between endothermic and exothermic reactions? _______________________________________________________Endothermic reaction take in heat _______________________________________________________from their surroundings whereas _______________________________________________________exothermic reactions give out heat _______________________________________________________to their surroundings. _______________________________________________________ Practical 1: Practical 2: 1. Fill a test tube 1/3 with 1. Fill test tube 1/3 water Copper sulfate 2. Add 1 spatula of Sodium 2. Record the temperature Bicarb 3. Add a 2cm length of 3. Record the temperature magnesium ribbon 4. Add 1 spatula of Citric acid 4. After 1 minute, record the 5. After 1 minute, record the temperature. temperature. Results: 5 degree temperature Result: 7 degree temperature Practical 1 increase decrease ExothermicThis reaction aswas the ____________. temperature I knowincreased. this because… _________________________________________________ _________________________________________________ Practical 2 This reaction was ____________. I know this because… Endothermic as the temperature decreased. _________________________________________________ _________________________________________________ Endothermic reactions Reaction Start Temp (oC) End Temp (oC) Temp Change (oC) Exo or Endo A 22.0 33.4 B 18.6 41.7 C 24.3 19.5 D 6.1 21.7 E 22.0 -3.6 F -12.2 2.3 How can you tell this reaction is endothermic? _______________________________________________________ _______________________________________________________ This reaction is endothermic because the energy of _______________________________________________________ the products is more than the energy than the _______________________________________________________ reactants. Energy has been taken in. _______________________________________________________ Endothermic or Exothermic? 1. Which type of reaction gives out energy to the surroundings? 2. Thermal decomposition is an example of … 3. Combustion is an example of… 4. Which type of reaction causes the temp of the surroundings to decrease? 5. An Ice pack is an example of… use a polystyrene cup better insulator ✓ ✓ ✓ 15.8 16.1 21.4 Lesson 3: Investigating endothermic Reactions In and On: Is this reaction endothermic or exothermic? ________________________________________________________________________ Challenge: How do you know?_______________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ Method: 1. Measure out 10 cm3 of water using a measuring cylinder. Record the starting temperature of the water in your results table 2. Collect a polystyrene cup with a pre weighed amount of potassium chloride in it. Record the mass to the appropriate number of decimal places in the table. 3. Add the water to your cup. Record the lowest temperature shown on your thermometer and record this answer to the appropriate number of decimal places. 4. Calculate the change in temperature. What are the variables for this experiment? Independent____________________________________________________________Independent – Mass of potassium chloride (g) Dependant______________________________________________________________Dependent – Temperature Control_________________________________________________________________Control – Volume of water, same polystyrene cup, length of Masstime of Start temperature End temperature Change in temperature potassium (oC) (oC) (oC) chloride (g) 2 24 22 2 4 24 20 4 6 24 18 6 8 24 16 8 10 24 14 10 Drawing graphs • Independent variable always goes on the x axis (horizontal) • Dependent variable always goes on the y axis (vertical) • Remove any anomalous results • Ensure you have a title • Ensure you have labelled each axis and state the unit • Ensure gaps are uniform ie. Every square is equal to 2 degrees Celsius • Draw a line of best (either with a ruler or a curve – do NOT join the points) Conclusion: _______________________________________________________________________ _______________________________________________________________________The more marble chips added to the acid, the greater the _______________________________________________________________________temperature increase. This is an exothermic reaction. _______________________________________________________________________ _______________________________________________________________________ Challenge: Why did you use a polystyrene cup rather than a beaker? _______________________________________________________________________The polystyrene cup provides greater insulation than a beaker. _______________________________________________________________________ How could you improve the experiment to make your results more reliable? _______________________________________________________________________ _______________________________________________________________________Carry out the experiment 3 times and take an average of your _______________________________________________________________________results. Additional notes: _________________________________________________ _________________________________________________ _________________________________________________ _________________________________________________ _________________________________________________ _________________________________________________ _________________________________________________ _________________________________________________ _________________________________________________ _________________________________________________ _________________________________________________ _________________________________________________ _________________________________________________