Signs of Chemical Reactions

Tell the difference between changes which are PHYSICAL and those which involve a CHEMICAL reaction Doing six different experiments and observing the changes which occur when substances react. We can tell whether something is a chemical reaction or physical change and can state some common signs of chemical reactions.

Stations

Exit Task Match Up Match the word to the definition. Precipitate Effervescence A chemical reaction in which heat is taken in. A chemical reaction in which heat is released. Exothermic Endothermic Bubbling and fizzing as a gas escapes from an aqueous solution A solid created in a solution during a chemical reaction.

Lesson 2 Energy Changes NEW LEARNING I can collect and analyse experimental data on chemical reactions that result in an obvious change in energy. I can apply my findings to explain the significance of the energy changes associated with chemical reactions. SCN 4-19a

Starter Questions 1 Name any one sign of a chemical reaction. Appearance change, temperature change, new substance formed, effervescence, precipitation. 2 Name one sign of a chemical reaction which can be seen in the diagram below Colour change, New substances formed (copper oxide and carbon dioxide), Gas given off

Starter Questions 3. When a fire is burning, is energy taken in or given out? Given out 4. How do you know? You can feel the heat from the fire reaching you and heating you up.

Energy Changes Today we will learn to State that chemical reactions have changes in energy. We will do this by Trying experiments to observe different types of energy changes. Learning about what the different types of energy changes are called. We will have succeeded if We can use the results of experiments to state whether a chemical reactions is exothermic or endothermic.

Energy changes When chemical reactions occur there is a change in energy When energy is given out, it is called an exothermic reaction When energy is taken in, it is called an endothermic reaction

Exothermic Reactions 1. Place the thermometer in the beaker and record the temperature. 2. Soak a piece of steel wool in vinegar for 1 minute. 3. Squeeze the excess vinegar out of the steel wool. 4. Wrap the wool around the thermometer and place the wool/thermometer in the beaker, sealing the lid. 5. Allow 5 minutes, then read the temperature and compare it with the first reading.

Endothermic Reaction 1. Pour the citric acid solution (20cm 3 ) into a styrofoam coffee cup. Use a thermometer or other temperature probe to record the initial temperature. 2.Stir in the baking soda (2 spatulas sodium bicarbonate). Track the change in temperature every 30 seconds What happens?

Elephant s toothpaste 1. Pour ~50 ml of 30% hydrogen peroxide solution into the graduated cylinder. 2. Squirt in a little dishwashing detergent and swirl it around. 3. You can place 5-10 drops of food coloring along the wall of the cylinder to make the foam resemble striped toothpaste. 4. Add ~10 ml of potassium iodide solution. You may touch a glowing splint to the foam to relight it, indicating the presence of oxygen.

More Energy Changes Hot Ice Sodium acetate or hot ice is an amazing chemical you can prepare yourself from baking soda and vinegar. You can cool a solution of sodium acetate below its melting point and then cause the liquid to crystallize. The crystallization is an exothermic process, so the resulting ice is hot. Solidification occurs so quickly you can form sculptures as you pour the hot ice. http://chemistry.about.com/od/homeexperiments/a/make-hot-ice-sodium-acetate.htm

Energy Changes Exit Task 1 In an exothermic reaction: A B C The temperature goes up The temperature goes down The temperature stays the same 2 Endothermic reactions: A B C Release energy to the surroundings Absorb energy from the surroundings Do not transfer energy to or from the surroundings

Lessons 3 & 4 Factors Affecting Reaction Rate

Change the speed of a chemical reaction using 3 different methods. We will also remind ourselves about Catalysts. Doing experiments in groups and changing the temperature, concentration or particle size of the chemicals we are using. Discussing catalysts and their uses. We can prove by experiment the effect of changing the temperature, concentration or particle size on the rate of reaction. We can state the definition of a catalyst and give some examples.

Particle Size Time taken for bubbling to stop (seconds) As particle size increases the rate of reaction decreases.

RESULTS Draw a table containing your results here. Temperature of acid ( O C) Time taken for magnesium to fully react (seconds) CONCLUSION Write how temperature affected reaction rate here. As temperature increases the rate of reaction increases.

Investigating Concentration AIM To investigate the effect of concentration on reaction rate. HYPOTHESIS (what I think will happen) Write your idea here METHOD -

Investigating Concentration RESULTS Draw a table containing your results here. Concentration (mol l -1 ) Time taken for cross to disappear (seconds) CONCLUSION Write how concentration affected reaction rate here. As concentration increases the rate of reaction increases.

Tell me three things... One you have done well One you would like to find out more about One you know now that you didn t know 50 minutes ago

Lessons 3 & 4 Factors Affecting Reaction Rate

Starter Questions 1. What does a catalytic converter do? Converts harmful exhaust gases into less harmful gases. 2. Which metal is a catalytic converter made of? Platinum (or rhodium or palladium) 3. What types of pollutants come out of car exhausts without a catalytic converter? Carbon monoxide, oxides of nitrogen, unburned hydrocarbons.

Lessons 5 Catalysts & Enzymes

Describe catalysts and enzymes and how they work. Discussing different catalysts and enzymes and their uses. Watching a video clip about catalytic converters in cars. Carrying out an experiment using a catalyst and an enzyme. We can state the definition for a catalyst and for an enzyme. Name an example of each and the reaction they catalyse.

An enzyme is a biological catalyst. It speeds up chemical reactions in living things and can be recovered unchanged at the end of the reaction (it is not used up in the reaction). Catalysts & Enzymes A catalyst is a substance which speeds up a chemical reaction and can be recovered unchanged at the end of the reaction (it is not used up in the reaction).

Common Catalysts Some common catalysts and the reactions they catalyse are: Catalyst Iron Platinum Reaction catalysed Making ammonia from nitrogen and hydrogen Car exhaust (oxides of nitrogen and carbon monoxide into nitrogen and carbon dioxide) Manganese dioxide Decomposition (breakdown) of hydrogen peroxide into oxygen and water

Common Enzymes Some common enzymes and the reactions they catalyse are: Enzyme Amylase Zymase Catalase Reaction catalysed Breakdown of starch into sugars e.g. glucose Brewing (fermentation) of sugar e.g. glucose into alcohol (ethanol) Decomposition (breakdown) of hydrogen peroxide into oxygen and water

Exit Task Matthew added 0.1g manganese dioxide to hydrogen peroxide solution and oxygen was produced. Manganese dioxide is a catalyst. 1. What is a catalyst? A catalyst is a substance which speeds up a chemical reaction and can be recovered unchanged at the end of the reaction (it is not used up itself). 2. What will be the mass of the manganese dioxide at the end of the reaction? 0.1 g (A catalyst is not used up in a reaction). 3. What would happen to the rate at which oxygen gas is given off if the temperature was raised to 35 o C? The rate of oxygen gas production will increase.

Question 1 Lesson Starter Which reaction will be faster: 1g marble lumps with acid or 1g marble powder with acid? 1g marble powder with acid

Question 2 Lesson Starter Which reaction will be faster: magnesium ribbon with concentrated acid or magnesium ribbon with dilute acid? With CONCENTRATED acid

Question 3 Lesson Starter At which temperature will the reaction between marble powder and acid be faster? 40 o C

Lesson 6 What Is Reaction Rate?

Carrying out a simple experiment to see how the speed/rate of a reaction varies with time. Watching the GLOW video to see how we can measure the RATE not just the relative SPEED of a chemical reaction. We can describe at least one experimental method of measuring the rate of reaction and can explain why this method is better than just timing how long it takes for a reaction to finish.

Observing Changes in Reaction Rate Set up the simple experiment shown below and make observations about how fast the reaction rate is at the start and as the reaction proceeds. Were the bubbles of gas produced just as quickly throughout the whole experiment? (If not describe how the rate of bubbling changed as the reaction proceeded).

Total mass of product (grams) The Rate Changes The rate of a chemical reaction changes as the reaction proceeds. The rate is faster at the beginning then slows down until eventually the reaction stops. We can measure this in a reaction rate experiment and plot a graph in which steepness of slope is linked to rate. Reaction is finished: no reactants left, all changed into products Rate is slower: less reactants left as some changed into products Rate is fast: lots of reactants Time (minutes)

Exit Task Consider a reaction between marble chips and acid what do you think the main difference between measuring overall speed of reaction and measuring rate might be? Why might it be more useful/better to measure the rate of reaction? HINT consider how many measurements you take for each? MEASURING OVERALL SPEED OF REACTION MEASURING RATE OF REACTION One measurement: Time taken to stop bubbling Several measurements: Mass of gas lost OR Volume of gas collected over time (e.g. every minute) until bubbling stops.

Lessons 7 & 8

Planning an investigation, noting down the method and the measurements/results we need to take and then completing an investigation report and graph of our results. Our plan allows us to carry out the investigation in a safe and organised way. The results collected allow us to make a valid conclusion on how varying the concentration of hydrochloric acid affects its rate of reaction with magnesium ribbon.

Experimental Report 1. Aim To investigate the effect of concentration on the rate of reaction of hydrochloric acid with magnesium. 2. Method Draw a diagram State which masses/volumes you will use Explain how you will measure the rate 3. Results Use a table to record your results e.g. Time (s) Concentration of Acid (mol l -1 ) 4. Conclusion : What do your results tell you?

LESSON STARTER TASK

Lessons 7 & 8

What? How? Explain what you have learnt today and how you have learnt it?

Planning an investigation, noting down the method and the measurements/results we need to take and then completing an investigation report Our plan allows us to carry out the investigation in a safe and organised way. The results collected allow us to make a valid conclusion on how varying the concentration of hydrochloric acid affects its rate of reaction with magnesium ribbon.

Lesson 9

Using these to decide what makes a GOOD investigation. We will then mark some sample investigations using our agreed key features and a rubric marking scheme. We can successfully mark a sample investigation by using our agreed key features and a rubrik marking scheme. We have a clearer idea of how to carry out a good investigation from now on.

PLUSS checklist used (Points, Labels, Units, Size & Scale) Correct type of graph must have been drawn line for number vs number data bar for word vs number data It contains an aim, hypothesis, method, results and conclusion. Also desirable is an evaluation. All results & observations recorded. The investigation should have been considered & planned out (with a data table and the variables to be changed and controlled noted down before experimental work starts). The report should be neat, organised and clear, containing all the key information. Experiment should be carried out in an organised, accurate and safe way then cleared up safely.

Investigation Marking Working In Pairs Use the Rubrik and your new knowledge of what makes a good investigation to mark the sample investigations completed by other S3 pupils. Complete two stars and a wish for each investigation marked. THEN As A Class We will compare the marks awarded to each investigation. This will allow us to assess our understanding of what makes a good investigation.

Rate your understanding of today s lesson using your fingers. Fist to Five

Lesson 10

Lesson starter A B C Time (minutes) 0.0 0.00 0.5 0.36 1.0 0.52 2.0 0.70 3.0 0.80 4.0 0.86 5.0 0.86 Mass lost (grams) D E Match the correct name to each graphic type shown above: Table Bar graph Flowchart Line graph Pie chart C D A E B

We can select the most appropriate type of graph to draw for our data and describe the features of a good graph.

Correct type of graph must have been drawn line for number vs number data bar for word vs number data Points plotted correctly (1/2 box tolerance allowed) Scale is appropriate and increases in a regular pattern. Labels included on both axes Units included if available. Size is appropriate to allow the data to be read

We can select the most appropriate type of graph to draw for our data and describe the features of a good graph.

Lessons 11 & 12 Interpreting Graphs

Learning Objectives & Success Criteria Today we will learn to Interpret graphs used to measure the rate of reaction and understand the changes to these graphs which can result from changing certain experimental factors. We will do this by Plotting graphs of experimental data in which certain variables have been altered. Studying our graphs and learning what the features tell us about the reaction rate. We will have succeeded if We can interpret information about a reaction from a reaction rate graph. We can predict the effect of altering an experimental variable on the shape of a reaction rate graph.

Total mass of product (grams) The Rate Changes Rate is fast: lots of reactants Reaction is finished: no reactants left, all changed into products Rate is slower: less reactants left as some changed into products Time (minutes) As the reaction proceeds the concentration of reactants decreases. This means less collisions of the reactants (i.e. less reactions). The reaction therefore slows down and the graph levels off.

Monitoring Reaction Rate This means measuring the rate of change in the quantity of a reactant or a product over a period of time. Consider a reaction in which marble chips (calcium carbonate) react with dilute hydrochloric acid. In this reaction we could attempt to measure the quantity of either of the two reactants used up or the quantity of any of the three products made over a period of time. BUT not all changes to the quantity of reactants and products are actually easy to measure.

Methods of Monitoring Reaction Rate 1 2 3 4 Measure the mass of gas product lost 5

Graphs of Reaction Rates Consider a reaction in which marble chips (calcium carbonate) react with dilute hydrochloric acid producing carbon dioxide gas.

Slope A B indicates the reaction rate. When the graph levels off at height C the reaction is complete The steeper the slope the faster the reaction. The quantity of product(s) formed is limited by the quantity of reactants (so if two curves level off at the same place that means the same quantity of reactants were used in both experiments).

Altered Variable Reaction Rate Graphs What can we do to each of our three experimental variables to get the increased reaction rate as shown in the graph? Decrease particle size Increase concentration Increase temperature What can we do to each of our three experimental variables to get the decreased reaction rate as shown in the graph? Increase particle size Decrease concentration Decrease temperature

Reaction Rate Extras There are two Interpreting Reaction Rate - Graph Exercises available (with an extra help sheet for exercise 1 if required). There is an animated reaction rate graph PPT. In the slides which follow this one there is also a rate graph quiz.

Reaction Rate Graph Quiz Graph B

Graph A

Graph B

Graph A

Reactions of zinc with excess hydrochloric acid Curve P was obtained using 1g zinc powder and 1 mol/l acid at 20 0 C Curve S Which curve could have been obtained using 1g zinc powder and 1 mol/l acid at 10 0 C?

Reactions of zinc with excess hydrochloric acid Curve P was obtained using 1g zinc powder and 1 mol/l acid at 20 0 C Curve Q Which curve could have been obtained using 0.5g zinc powder and 1 mol/l acid at 20 0 C?

Reactions of zinc with excess hydrochloric acid Curve P was obtained using 1g zinc powder and 1 mol/l acid at 20 0 C Curve R Which curve could have been obtained using 1g zinc powder and 1 mol/l acid at 30 0 C?

Reactions of zinc with excess hydrochloric acid Curve P was obtained using 1g zinc powder and 1 mol/l acid at 20 0 C Curve S Which curve could have been obtained using 1g zinc lumps and 1 mol/l acid at 20 0 C?