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level: 6.1

Questions and Answers List

level questions: 6.1

QuestionAnswer
A positive sign on a reaction pathway diagram showsEndothermic reactions
Activation energy always has a positive value of enthalpy change, why?Because enough energy has to be absorbed
Activation energy always has a positive value of enthalpy change, why?Because enough energy has to be absorbed
A positive sign on a reaction pathway diagram showsEndothermic reactions
Chemical reaction that transfer heat to surroundings are described as?exothermic
Chemical reactions that absorb heat energy from surroundings are described as?endothermic
In exothermic reactions, temperatures of surrounding increases. Theses surroundings include (4)? Give 3 examples of exothermic reactions.Surroundings include - Solvent - Air around test -tube - Test tube itself - Anything dipping into the test-tube Examples of exothermic reactions include 1. Combustion of fuels 2. Oxidation of carbohydrates in bodies of animals and plants (respiration) 3. Reaction of water with quicklime (calcium oxide)
What are 3 examples of endothermic reactions1. Decomposition of limestone by heating (all thermal decompositions are endothermic) 2. Photosynthesis 3. Dissolving certain ammonium salts in water
Energy change between a chemical reaction and its surroundings at constant pressure is called theEnthalpy change
What is EnthalpyEnthalpy is the total energy associated with materials that react
What is the symbol for enthalpyH
Cannot measure enthalpy, but we can measure an enthalpy change when heat energy is exchanged with surroundings. We write this as:Enthalpy change = change of product - enthalpy of reactants
What are the units for enthalpy changekilojoules per mole (Kj mol^-1)
What are the diagrams called that show enthalpy changes?Reaction pathway diagrams / enthalpy profile diagrams
On Reaction pathway diagrams what is shown on the y-axis and what is shown on the x-axisy-axis = enthalpy of reactants and products x-axis = Reaction pathway, wuth reactants on the left and products on the right
Reaction pathway diagrams usually also show (1) as a hump (up and down curve) between reactants and the productActivation energy Ea
What is activation energyActivation energy is the minimum energy that colliding particles must possess for a reaction to happen
Activation energy always has a positive value of enthalpy change, why?Because enough energy has to be absorbed to increase the kinetic energy of reactant molecules so that they collide with enough force to break bonds
For exothermic reactions, enthalpy of reactants must be (< / >) the the enthapy of the productsGreater than
A negative sign on a reaction pathway diagram showsExothermic reactions
For endothermic reactions, the enthalpy of the product must be (< / >) than enthalpy of reactantsGreater than
A positive sign on a reaction pathway diagram showsEndothermic reactions