Paper 1- Physical Chemistry
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What is an exothermic reaction?
A reaction that gives out energy to the surroundings resulting in a rise in temperature of the surroundings -EXothermic- EXIT- gives out
What is an endothermic reaction?
A reaction that takes in energy from surroundings resulting in a decrease in temperature of the surroundings -ENdothermic-enter-take in
What is enthalpy change?
overall change in energy in a reaction
Does enthalpy change have a positive or negative value when the reaction is exothermic
• negative - as the reaction is giving out energy
Does enthalpy change have a positive or negative value when the reaction is endothermic
• positive - as reaction takes in energy
What is the rate of a reaction?
how fast the reactants are changed into products
Give an example of a slow reaction?
rusting of iron
Give an example of a moderate reaction?
metal magnesium reacting with an acid
Give an example of 2 fast reaction?
burning and explosions
How do you find speed of a reaction?
By recording the amount of product formed or amount of product used up over time
What does a steeper line on the graph show in terms of rate of reaction
fast reaction
What does the rate of a reaction depend on?
• collision frequency of reacting particles (the more collisions, the faster reaction) • energy transferred during a collision (particles have to collide with enough energy for the collision to be successful
What is activation energy?
the minimum amount of energy that particles need to react
Why do particles need activation energy?
-to break the bonds in the reactants and start the reaction
What four factors does the rate of reaction depend on?
• temperature • concentration • surface area • catalyst
How does increasing the temperature increase the rate of reaction?
• when temperature is increased particles move faster so will have more collisions • higher temp also increases energy of collisions, as particles are moving faster • meaning at higher temps there will be successful collisions • so increasing the temp increases rate of reaction
Explain why increasing concentration increases the rate of reaction
-if a solution is more concentrated it means there are more particles of reactant in same volume making collisions more likely so ROR increases
Explain why increasing pressure increases the rate of reaction
-increasing pressure in a gas means particles are more crowded so frequency of collisions between particles will increase
Explain why increasing surface area increases the rate of reaction
• breaking a solid into smaller pieces will increase its surface area to vol ratio • meaning particles around it will have more area to work on • meaning rate of reaction is faster for solids with a large surface area to vol ratio
What is a catalyst?
a substance which increases the rate of reaction without being chemically used up or changed in a reaction, -usually finds an alternate pathway
How do catalysts work?
• lower the activation energy by providing an alternative pathway that has a lower activitaion energy • as a result more particles have the minimum amount of energy needed for reaction to occur when particles collide
How can you show the effect of a catalyst
Reaction profiles
Name the equation used to measure the speed of a reaction
amount of reactant used or amount of product formed / time
Name the three rates of reaction experiments
• precipitation • change in mass • volume of gas given off