C2.5 Flashcards
What is an exothermic reaction
A reaction that increases the temperature of its surroundings
What are endothermic reactions
Reactions that cool down its surroundings
Give an example of an exothermic and an endothermic reaction
Any combustion is exothermic
CH4 + 2O2 —> H2O + CO2
Sodium hydrogencarbonate + hydrochloric acid
Photosynthesis
What causes endothermic and endothermic reactions
In a reaction, bonds are broken, energy is needed to break bonds in the form of heat, so this is endothermic. When new bonds are made in the reaction, heat energy is released, this is exothermic. In exothermic reactions, more energy is released than taken in when braking the bonds so there is an overall increase in temperature, and the opposite happens in endothermic reactions.
What would and exothermic reaction and an endothermic reaction look like in a graph
In exothermic, reactants will have a high y value if y axis is energy and reactants will have a low y value as they have released energy. Endothermic would be opposite, low to high
What is the rate of a chemical reaction
The speed in which new products are formed from reactants
What is concentration
The a,out of solute there is in a solvent
What must happen for a reaction to occur
The reactant particles must collide with enough force to break bonds in the reactants
Why does concentration increase rate of reaction
The higher the conc of a reactant there is, the more reactant particles there are in fixed amount of volume. As there are more, the reactant particles are more likely to collide with each other so the more collisions meaning a faster rate of reaction
How and why does temperature affect rate of reaction
Hotter it is, the more energy the reactant particles are so the faster they are moving. This means they collide more frequently and are more likely to have enough energy to break the bonds so greater rate of reaction.
How does surface area affect rate of reaction and why
Reactants only react when they collide, can’t collide if they are beneath other particles. By increasing surface area, you are increasing the amount of reactant particles on the surface of the solid so there are more reactant particles that can come into contact with the other reactant and react. So the greater the surface area, the greater the rate of reaction
What are catalysts
Chemicals/substances that increase rate of reaction without being used up
Why are catalysts good
They increase rate of production
They often decrease the temperature and pressure needed for the reaction which is cheaper and saves energy
What do catalytic converters do
They help react unburnt hydrocarbons and carbon monoxide in the car fumes with oxygen in the air to form carbon dioxide and water which is cleaner for the environment
What is the structure of a catalytic converter and why is it like it
It uses a honeycomb structure which gives it a very large surface area so can catalyse reactions quickly. It uses very thin layers of the catalyst on the structure as the metals used are expensive. The metals often used are platinum, rhodium or palladium
