Exothermic And Endothermic Reactions
Visão Geral
Strike a match and it gives out heat; mix the chemicals in a cold pack and they draw heat in. Every chemical reaction involves a change in energy, and whether energy is released or absorbed sorts reactions into two great families: exothermic and endothermic.
In this lesson you will learn what exothermic and endothermic reactions are, how to recognise them from temperature changes, and how energy level diagrams show the energy change. You will also see how breaking and making bonds explains where the energy comes from and goes.
Objetivos
- State that an exothermic reaction transfers thermal energy to the surroundings leading to an increase in the temperature of the surroundings.
- State that an endothermic reaction takes in thermal energy from the surroundings leading to a decrease in the temperature of the surroundings.
- Interpret reaction pathway diagrams showing exothermic and endothermic reactions.
- [Supplement] State that the transfer of thermal energy during a reaction is called the enthalpy change, ∆H, of the reaction. ∆H is negative for exothermic reactions and positive for endothermic reactions.
- [Supplement] Define activation energy, E , as the minimum a energy that colliding particles must have to react.
- [Supplement] Draw and label reaction pathway diagrams for exothermic and endothermic reactions using information provided, to include: (a) reactants (b) products (c) enthalpy change of the reaction, ∆H (d) activation energy, E a.
- [Supplement] State that bond breaking is an endothermic process and bond making is an exothermic process and explain the enthalpy change of a reaction in terms of bond breaking and bond making.
- [Supplement] Calculate the enthalpy change of a reaction using bond energies.
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- An exothermic reaction is one that: A. Takes in thermal energy B. Transfers thermal energy to the surroundings C. Has no energy change D. Always involves a gas Answer: B
- During an endothermic reaction, the temperature of the surroundings: A. Rises B. Falls C. Stays the same D. Doubles Answer: B
- On an energy level diagram for an exothermic reaction, the products are: A. Higher than the reactants B. Lower than the reactants C. At the same level D. Not shown Answer: B
- Breaking chemical bonds is: A. Exothermic (gives out energy) B. Endothermic (takes in energy) C. Neither D. Always impossible Answer: B
- A reaction where the temperature rises from 18 to 30 degrees Celsius is: A. Endothermic B. Exothermic C. Reversible D. Neutral Answer: B
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