energy changes
暂无描述。系统推荐的高质量记忆内容，适合每天坚持背诵学习。
卡片预览 (24 张)
define an exothermic reaction
a reaction that transfers energy to the surroundings, so the temperature of the surroundings increases. therefore, the product molecules have less energy than the reactants
examples of exothermic reactions
• combustion • many oxidation reactions • neutralisation
describe reaction profile of exothermic reactions
• reactants are at a higher energy than the products because energy has been transferred from the molecules to the surroundings (energy is lost to the surroundings) • negative energy change
everyday uses of exothermic reactions
• self-heating cans • hand warmers
define an endothermic reaction
a reaction that takes in energy from the surrounds so the temperature of the surroundings decrease. therefore, the reactant molecules have less energy than the products
examples of endothermic reactions
• thermal decompositions • reaction of citric acid and sodium hydrogencarbonate
describe reaction profile of endothermic reactions
• reactants are at a lower energy than the products because energy is taken in from the surroundings to the molecules (temperature of surroundings decrease) • positive energy change
everyday uses of endothermic reactions
• sports injury packs (cold packs)
define activation energy
the minimum amount of energy that particles must have to react (for a reaction to occur)
what for reaction profiles show
• the relative energies of reactants and products • activation energy • if its exothermic or if its endothermic • overall energy change
when is energy supplied and released during a chemical reaction
• energy must be supplied to break bonds in the reactants • energy is released when bonds in the products are formed
what is bond energy
it’s the energy needed to break bonds and the energy released when bonds are formed
how do you calculate overall energy change
• calculate the bond energies for the reactants and for the products energy change = energy of bond breaking - energy of bond making i.e. bond energy of reactants minus bond energy of products
what are the units for overall energy change
kJ/mol
define overall energy change
the difference between the sum of the energy needed to break bonds in the reactants and the sum of the energy released when bonds in the products are formed
describe making and breaking bonds in an exothermic reaction
the energy released from forming new bonds is greater than the energy needed to break existing bonds i.e. overall energy change will be negative
describe making and breaking bonds in an endothermic reaction
the energy needed to break existing bonds is greater than the energy released from forming new bonds i.e. overall energy change will be positive
define an electrolyte
a solution that can conduct electricity e.g. an ionic compound solution
how can you produce electricity using an electrolyte
by taking two different metals and placing them into an electrolyte
what do cells contain
chemicals which react to produce electricity
how is a simple cell made
it can be made by connecting two different metals in contact with an electrolyte
what is the potential difference produced by a cell dependent on
• type of electrode • type of electrolyte • concentration; the greater the concentration of ions in the electrolyte, the greater the potential difference produced
how do you provide a greater voltage
by connecting two or more cells together in series (batteries do this)
when will cells produce electricity
when there is a difference in reactivity between the two metals e.g., if they are the same metal, there will be no difference in reactivity, so no current will flow