Why is energy involved in chemical reactions

Calculate the temperature change for both chemical reactions. Based on your observations of the baking soda and vinegar reaction, is the reaction exothermic or endothermic? Apply your knowledge of energy changes in chemical reactions to complete the table above. Based on your observations of the baking soda solution and calcium chloride reaction, is this chemical reaction exothermic or endothermic? Interpreting Evidence.

In the chemical reaction between baking soda and vinegar, what did you observe other than a temperature change? What might this tell you about one of the products of this chemical change?

In the chemical reaction between baking soda solution and calcium chloride, what did you observe other than a temperature change? Use your answers from questions 1 and 2 to help you write the chemical equation for: the chemical reaction between baking soda and vinegar the chemical reaction between baking soda and calcium chloride Using the language of breaking and making bonds, explain the net energy change for the chemical reaction between baking soda and calcium chloride.

Draw energy profiles for both chemical reactions. Refer to the exothermic energy profile shown previously as an example. Are they the same or different? Reflecting on the Investigation. Based on your investigation so far, do you think that energy changes only accompany chemical reactions? Using only the materials from the first two reactions, design an experiment that would test this idea. Propose a procedure and have it approved by your teacher before you continue experimenting.

Is dissolving calcium chloride in water a chemical change? Explain your reasoning. Using the language of breaking and making bonds, how can you describe the temperature change you observed when you dissolved calcium chloride in water? How might you use exothermic or endothermic processes to solve a real-world problem?

Are there any instances when it would be useful to quickly make something hot or cold? Explain how it is useful to know which processes absorb or release energy.

The system is the specific portion of matter in a given space that is being studied during an experiment or an observation. The surroundings are everything in the universe that is not part of the system.

In practical terms for a laboratory chemist, the system is the particular chemicals being reacted, while the surroundings are the immediate vicinity within the room. During most processes, energy is exchanged between the system and the surroundings. If the system loses a certain amount of energy, that same amount of energy is gained by the surroundings. If the system gains a certain amount of energy, that energy is supplied by the surroundings. A chemical reaction or physical change is endothermic if heat is absorbed by the system from the surroundings.

In the course of an endothermic process, the system gains heat from the surroundings and so the temperature of the surroundings decreases. A chemical reaction or physical change is exothermic if heat is released by the system into the surroundings. Because the surroundings are gaining heat from the system, the temperature of the surroundings increases.

During phase changes, energy changes are usually involved. For example, when solid dry ice vaporizes physical change , carbon dioxide molecules absorb energy. When liquid water becomes ice, energy is released.

Remember that all chemical reactions involve a change in the bonds of the reactants. In energy producing exothermic reactions the total energy of the products is less than that of the reactants - energy is released to the surroundings.

Combustion and respiration in biological systems are the most obvious examples. Some exothermic reactions require some energy to get them started, but then they release more energy than was needed for initiation. A match requires initial energy, provided by the heat generated from the friction as it strikes the rough surface on the matchbox to ignite it. Once the match starts burning, it releases more energy than was required for ignition so the reaction is still exothermic.

The products still have less chemical energy than the reactants. In energy consuming endothermic reactions the total energy of the products is more than that of the reactants - heat is taken from the surrounding substances. The reactions involved in photosynthesis are perhaps the most important of these.

The production of aluminium is another important example of an energy consuming process. This has implications benefits and costs for energy use within Victoria. Explore the relationships between ideas about energy producing and consuming chemical reactions in the Concept Development Maps - Chemical reactions, Flow of energy in ecosystems, Flow of matter in ecosystems.

Because of widely held alternative conceptions in this area, students will need to observe and reflect on a wide range of chemical reactions which consume and produce energy. They will need to be encouraged to examine their existing views in the light of new evidence and to reflect on how these views have changed as a result of their investigations.

An initial activity could seek to establish existing student ideas about energy changes involved in burning. Students in small groups could be asked to draw a diagram of the burning of a candle and with arrows show the energy changes that take place. Due to the absorption of energy when chemical bonds are broken, and the release of energy when chemical bonds are formed, chemical reactions almost always involve a change in energy between products and reactants.

By the Law of Conservation of Energy, however, we know that the total energy of a system must remain unchanged, and that oftentimes a chemical reaction will absorb or release energy in the form of heat, light, or both. The energy change in a chemical reaction is due to the difference in the amounts of stored chemical energy between the products and the reactants.

This stored chemical energy, or heat content, of the system is known as its enthalpy. Exothermic reactions release heat and light into their surroundings. For example, combustion reactions are usually exothermic.