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What factors need to be controlled to make sure the comparison between fuels is reliable?

What factors need to be controlled to make sure the comparison between fuels is reliable?

Chemistry
Chemistry
10th Edition
ISBN:9781305957404
Author:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Publisher:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Chapter1: Chemical Foundations
Section: Chapter Questions
Problem 1RQ: Define and explain the differences between the following terms. a. law and theory b. theory and...
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What factors need to be controlled to make sure the comparison between fuels is reliable?

Energy Changes and Calorimetry Enthalpy Changes All substances contain chemical energy, called enthalpy. It is measured in Joules. When reactions happen, energy is given out or taken in – these are enthalpy changes. Endothermic and exothermic reactions In exothermic reaction, chemical energy (enthalpy) is being turned into heat energy which is transferred to the surroundings, so the temperature we measure increases. In endothermic reaction, heat energy is taken from the surroundings and converted into chemical energy (enthalpy), so the temperature decreases, or we have to heat the reaction constantly to make it work. When a reaction takes place, bonds in the reactants are broken, and new bonds formed in the products. The energy required to break all the necessary bonds in the reactants is called the activation energy. In an exothermic reaction less energy is used to break the bonds in the reactants than is released when the bonds in the products are formed. In anendothermic eaction more energy is used to break the bonds in the reactants than is released when the bonds in the products are formed. A catalyst increases the rate of reaction without being used up itself. It does this by lowering the activation energy for the reaction, by providing an alternative pathway. On the catalyst surface the reactants have their bonds weakened, so that less energy is needed to break these bond
Transcribed Image Text:Energy Changes and Calorimetry Enthalpy Changes All substances contain chemical energy, called enthalpy. It is measured in Joules. When reactions happen, energy is given out or taken in – these are enthalpy changes. Endothermic and exothermic reactions In exothermic reaction, chemical energy (enthalpy) is being turned into heat energy which is transferred to the surroundings, so the temperature we measure increases. In endothermic reaction, heat energy is taken from the surroundings and converted into chemical energy (enthalpy), so the temperature decreases, or we have to heat the reaction constantly to make it work. When a reaction takes place, bonds in the reactants are broken, and new bonds formed in the products. The energy required to break all the necessary bonds in the reactants is called the activation energy. In an exothermic reaction less energy is used to break the bonds in the reactants than is released when the bonds in the products are formed. In anendothermic eaction more energy is used to break the bonds in the reactants than is released when the bonds in the products are formed. A catalyst increases the rate of reaction without being used up itself. It does this by lowering the activation energy for the reaction, by providing an alternative pathway. On the catalyst surface the reactants have their bonds weakened, so that less energy is needed to break these bond
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