Energy Changes Flashcards
(18 cards)
What happens in exothermic reactions
Thermal energy is transferred from the chemical to the surroundings. As the thermal energy increase in the surroundings, the temperature increases so it gets hotter
Are most chemical reactions exothermic or endothermic
Exothermic
Examples of exothermic reaction s
Respiration in all cells
Combustion such as burning fuels
Neutralisation reactions such as acids reacting with alkalis
Formula for methane
CH4
Application of exothermic reaction for cold places for humans
Hand warmers to keep hands warm
Application of exothermic reaction for food and drink
Self heating fans. In these cans the food or drink is Seperated by a layer containing the chemicals used for heating. This is often calcium oxide and a bag of water. When a button is pressed by the user, the bag of water is punctured and mixed with the calcium oxide. They react to cause an exothermic reaction and release thermal energy which heats up the food or drink.
What happens in endothermic reactions
Thermal energy is transferred from the surroundings to the chemicals. As there is less thermal energy, the temperature decreases and get cooler.
Three applications of endothermic reactions
Sports injury packs - a bag of water and ammonium nitrate react when these bag is squeezed and water bag hurts and ammonium nitrate dissolves in the water.
Decomposition such as thermal decomposition of metal carbonates
Reaction of acids with metal hydrogencarbonates
What is activation energy
The minimum energy particles must have to react
When can chemical reactions only occur
When particles collide with each other with enough energy to react
Where is activation energy on reaction profile
From reactants to highest point of the loop
Is an exothermic reaction on a reaction profile when the reactants are higher (have more energy) than products or when reactants are lower than products
When reactants are higher than products
Where is overall energy change shown on reaction profile
Draw a line from the axis that the reactant is to the axis where the products is
Does breaking bonds require or release energy
It requires energy
Does making bonds require or release energy
It releases energy
What happens with energy in a chemical reaction
Energy must be supplied to break bonds in the reactant and energy is released when the ponds in the product are made
Equation for energy change
Energy change = energy need breaking bonds in reactant - energy released making bonds in products
Which elements are diatomic
Have no fear of ice cold biryani
