6 March 2013 Give an example of a physical change and a chemical change, and then describe how they are different from the other. Explain your answer in 2-3 sentences.
Standards 8.5.c. I know chemical reactions usually liberate or absorbs heat.
When chemical reactions occur, the connections between atoms must be broken and rearranged. In order to do this, Heat is involved in all chemical reactions.
Endothermic Within-Heating Endo = Enter Therm/ic = Heat Exothermic Outside-Heating Exo = Exit Therm/ic = Heat
Endothermic Reactions in which the system absorbs heat from the surrounding. Exothermic Reactions in which the system releases heat to the surrounding.
Endothermic It feels: Cold It feels: Exothermic Hot
Endothermic Examples: Cooking an egg Baking a bread Exothermic Examples: Candle flame Rusting Iron
Exothermic Reaction
Endothermic Reaction
Heat (Thermal Energy) in phase change is not the same as Heat of Reaction. Phase Change = Physical Change Chemical Reaction = Chemical Change
Example Cooking Egg Baking of cake Activation of cold pack Non-Example Heat of melting Heat of vaporization Heat of sublimation
Example Candle burning Explosion of dynamite Activation of yeast Non-Example Heat of deposition Heat of freezing Heat of condensation
6 March 2013 In your own understanding, what causes steel to rust. Explain your answer in 2-3 sentences.
Minimum amount of energy needed to start a chemical reaction All reactions require a certain amount of activation energy.
Surface Area Temperature Concentration Presence of catalyst or inhibitor
Factors Effects Surface Area The greater the area exposed, speed up the reaction. Speeding up reactions are both useful and harmful. Useful: chewing food to make it easy to digest. Harmful: gas fumes or dust particles ignites easily.
Temperature Increasing the temperature, increases the movement of the particles and energy. Decreasing the temperature, decreases the movement of the particles and energy. Something good to remember: We store food in the refrigerator to lower the temperature and slowdown the reaction in spoiling food.
Concentration It is the amount of stuff(substance) in a given volume. Example: Adding more sugar in coffee increases the concentration of sugar (sweeter). Adding more lemon juice in lemonade increases the concentration of acidity (sourness).
Catalyst A material added to reduce the activation energy. Example: Lead and Sulfur as fuel additive Enzymes are examples of catalyst found in the human body.
Inhibitors A material added to reduce the rate of reaction. Examples: Food preservatives Lubricant/protective coating
Is popping popcorn a physical change or a chemical change? Explain your answer. Due: March 01, 2013
Objective: Observe a chemical reaction. Observe an endothermic reaction.
1.3 grams citric acid (H3C6H5O7) 1.5 grams Baking Soda = Sodium Bicarbonate (NaHCO3) Zip-lock bag Small cup Electronic scale Graduated cylinder Weighing plate 20 ml H 2 O
H 3 C 6 H 5 O 7 + 3NaHCO 3 Citric acid + sodium bicarbonate CO 2 + 3H 2 O + NaC 6 H 5 O 7 carbon + water + sodium citrate dioxide
Procedure: Place weighing plat on scale press zero so that scale doesn t measure the mass of the weighing plate. Measure 1.5g sodium bicarbonate (baking soda) onto the plate. Add to plastic bag. Measure 1.3g citric acid onto plate. Add to plastic bag. Using the graduated cylinder, measure 20 ml of H 2 O. Pour the water into the small cup. Place the cup inside the plastic bag standing up. Be careful not to spill the water! Carefully squeeze the air out of the bag and zip the bag tightly shut. Tip the cup over to spill the water and mix ingredients with your hands. Record your observations below in the data section. Clean your lab station and answer discussion questions below.
Reactants Elements in Reactant Observations Citric Acid Sodium Bicarbonate
What do you SEE happening during the reaction? What do you FEEL happening during the reaction?
1. Do you think this was a physical or chemical reaction? What is your evidence? 2. What do you think was produced in this reaction? What is your evidence? 3. From what you observed and felt during the reaction do you think energy was going into the reaction (being used up) or out of the reaction (heat is being produced)? What is your evidence? 4. From what you observed in today s lab, what do you think an endothermic reaction is? 5. What is one question you have about this experiment? (write AT LEAST 1 question)
Objective: Observe a chemical reaction. Observe an exothermic reaction.
Materials: 1.5 grams yeast 20 ml hydrogen peroxide (H 2 O 2 ) Zip-lock bag Small cup Electronic scale Graduated cylinder Weighing plate
Procedures 1. Place weighing plat on scale press zero so that scale doesn t measure the mass of the weighing plate. 2. Measure 1.5g yeast onto the plate. Add to plastic bag. 3. Using the graduated cylinder, measure 20 ml of H 2 O 2. Pour the hydrogen peroxide into the small cup. 4. Place the cup inside the plastic bag standing up. Be careful not to spill! 5. Carefully squeeze the air out of the bag and zip the bag tightly shut. 6. Tip the cup over to spill the hydrogen peroxide and mix ingredients with your hands. 7. Record your observations below in the data section. 8. Clean your lab station and answer discussion questions below.
Reactants Hydrogen Peroxide Elements in Reactant Observations Yeast (this is a type of cell and has LOTS of elements)
What do you SEE happening during the reaction? What do you FEEL happening during the reaction?
1. Do you think this was a physical or chemical reaction? What is your evidence? 2. What do you think was produced in this reaction? What is your evidence? 3. From what you observed and felt during the reaction do you think energy was going into the reaction (being used up) or out of the reaction (heat is being produced)? What is your evidence? 4. From what you observed in today s lab, what do you think an exothermic reaction is? 5. What is one question you have about this experiment? (write AT LEAST 1 question)
How can you tell if a chemical reaction is endothermic or exothermic? What are common daily events involving endothermic or exothermic reactions? Name at least 2 examples per type, then support your answer by paraphrasing the concepts you learned? Why are reactions (exothermic and endothermic) important to our existence?
Sugar dissolving in tea Chemical Change Physical Change
Logs burning Chemical Change Physical Change
Breaking water up by separating it into hydrogen and oxygen Chemical Change Physical Change
Cutting paper Chemical Change Physical Change
Crushing an aspirin Chemical Change Physical Change
Metal rusting Chemical Change Physical Change
An egg rotting Chemical Change Physical Change
An egg breaking Chemical Change Physical Change