Activity Hot and Cold

Name:_______________________ Per:____ Activity- Hot and Cold goggles must be worn Introduction: Virtually every chemical reaction & physical change involves the absorption or release of heat energy. The combustion of methane gas is an obvious example of a reaction that releases heat energy. Ice cubes melting, water vapor condensing into a liquid, and the dissolving of salts into a solution also absorb and release energy. A process that gives off heat to the surroundings is called exothermic. Ex: CH4(g) + 2O2(g) CO2(g) + 2H2O(l) + heat (890.3 kJ) A process that absorbs the energy of the surroundings is called endothermic. Ex: NaCl (s) + heat (411 kJ) <--> Na+ + ClPurpose: a) track the exchange of energy that always occurs when matter is altered b) learn what the symbol ∆T means and how it’s calculated c) identify reactions as endothermic or exothermic. Data table/ Observations: Temp Temp initial final Salt added to 10 mL of water 1 g NaOH 1 g NaCl 1 g NH4NO3 of H2O (°C) of solution (°C) Temp. change (∆T) = Temp final-Temp initial Observations when touched with hand Calculations/ Analysis: 1. Which of the three processes that you carried out is/are exothermic? Explain. 2. Which of the three processes that you carried out is/are endothermic? Explain. 3. Identify if each of these reactions are endothermic or exothermic & how you know. a. H2 + O2  H2O + 483.6 kJ (heat) b. H2O + 483.6 kJ (heat)  H2 + O2 The temperature change is ∆T, pronounced “delta T.” You find it by calculating the final temperature minus the initial temperature. 4 a. The temperature of a solution started at 25 °C and then went up to 50°C. Calculate the ∆T. (show work) b. Is the reaction endothermic or exothermic? Explain. c. Convert the above temperatures (in 4a)to Kelvin and calculate the ∆T in Kelvin. (show work) d. How does the ∆T differ when using the temperatures in °C vs. Kelvin? Do you think it matters which we use? 5 a.The temperature of a solution started at 50 °C and then went down to 25°C. Calculate the ∆T. (show work) b. Is the reaction endothermic or exothermic? Explain. 6. a. b. 7. a. Match Burning Draw arrows on the match/ environment surrounding the match to show the direction heat is being transferred. From the perspective of the match (where combustion is occurring), is fire an endothermic or exothermic process? Explain. Injured Foot being Iced Indicate with arrows (on picture)the direction in which heat is being transferred. b. c. From the foot’s perspective, is putting ice on an injury an endothermic or exothermic process? Explain From the ice pack’s perspective, is the process an endothermic or exothermic process? Explain. d. There is no such thing as cold. Cold is a “feeling” but is not a "thing" that can be transferred from one place to another. What is really happening when you feel the cold icepack on your foot? e. 8. Does your body sense temperature changes the same as a thermometer does? Explain. Coffee left on counter all night a. Indicate with arrows (on image) the direction in which heat is being transferred. b. To the coffee, is this process endothermic or exothermic? Explain. c. What will be the temperature of the coffee be in the morning? Explain. d. Would your body come to thermal equilibrium with the classroom (like the coffee did) if you stayed in it all night? Why or why not? 9. The temperature decreases when you put thermometer in ice water a. Indicate with arrows the direction heat transfers between thermometer & the solution. b. What would your hand experience if it came into contact with the solution? Why? c. When the ice dissolves, heat is absorbed by the solution yet the thermometer shows a temperature decrease. How can this be? 10. In general, which way does heat move? When does heat transfer stop between two objects? Ice water 11. In order to decide if something is endo/exothermic, it’s important to know whose perspective you are taking. Why? Whose do we normally take in chemistry? Procedure: AT YOUR LAB STATIONS 1. Using a graduated cylinder, add 10 mL of water to a test tube 2. Measure the temperature of the water and record it (Temp initial). 3. Add 1 g of NaOH, sodium hydroxide, to the water and stir with a stirring rod. 4. Quickly place the thermometer in the solution. Record the highest temperature you observe (Temp final). Feel the outside of the beaker with your hand. 5. Repeat the procedure for NaCl, sodium chlroide, & Repeat with NH4NO3, ammonium nitrate. Discard of All substances in waste containers in the front of the room!! Procedure: AT YOUR LAB STATIONS 1. Using a graduated cylinder, add 10 mL of water to a test tube 2. Measure the temperature of the water and record it (Temp initial). 3. Add 1 g of NaOH, sodium hydroxide, to the water and stir with a stirring rod. 4. Quickly place the thermometer in the solution. Record the highest temperature you observe (Temp final). Feel the outside of the beaker with your hand. 5. Repeat the procedure for NaCl, sodium chloride, & Repeat with NH4NO3, ammonium nitrate. Discard of All substances in waste containers in the front of the room!!