Rates of Reaction and Energy Changes

How does increasing concentration affect the rate of reaction?

If there are more particles then there will be a higher number of successful collisions

How does increasing temperature affect the rate of reaction?

• The particles gain energy, making them move faster, leading to a higher amount of collisions quickly

• The particles hit harder so the collision has a higher chance of being successful

How does increasing surface area affect the rate of reaction?

If something has a larger surface area, there are more places for particles to collide with, leading to more successful collisions

What is the meaning of the rate of reaction?

The speed at which reactants are turned into products

What term should we use when talking about chemical reactions making products?

Successful collisions

Why will a reaction slow down near the end?

Because there are less reactants than what we started with as they were all used up

What do we call a substance that can speed up the rate of reaction?

A catalyst

Why are catalysts useful?

• They reduce activation energy so high temperatures aren’t needed

• They are never used up which saves money

• They speed up the rate of reaction

• They don’t alter the products of a reaction

If we know that increasing surface area increases the rate of reaction, why would a powder react faster than a larger chunk of a substance?

Because the powder is grinded up into smaller pieces, there is a larger overall surface area so there are more surfaces for successful collisions to occur

What is an exothermic reaction and what will happen to bond in an exothermic reaction?

• A reaction that gives off heat

• Energy is transferred to the surroundings as bonds form, so making bonds is exothermic

What is an endothermic reaction and what happens to bonds in one?

• A reaction which takes in heat

• Energy is transferred to the reactants to break their bonds, so breaking bonds in endothermic

What happens to the temperature of surroundings in an exothermic reaction?

Temperature of surroundings increases

What happens to the temperature of surroundings in an endothermic reaction?

Temperature of surroundings decreases

How do we calculate bond energy?

1. Calculate energy in (Bonds broken)

2. Calculate energy out (Bonds made)

3. Energy Change=energy in - energy out

4. A negative answer=exothermic and a positive answer=endothermic

What are the requirements for a reaction to happen?

• The reactant particles must collide with each other

• The collisions must have enough energy

What is activation energy?

The minimum energy needed by reactant particles for a reaction to happen

How does increasing pressure increase the rate of reaction?

• There are more particles in the same volume

• The frequency of successful collisions increases

What should we see in an exothermic reaction profile?

• The energy level of the reactants is greater than the energy level of the products

• The energy change of the reaction is negative ( energy is transferred to the surroundings)

What should we see in an endothermic reaction profile?

• The energy level of the reactants is lower than the energy level of the products

• The energy change of the reaction is positive (energy is transferred from the surroundings to the products)

How can activation energy be supplied?

• Heating the reaction mixture

• Applying a flame or spark

• Continually Heating the reaction mixture

• Passing an electric current through an electrolyte (as in electrolysis)

What is bond energy?

The energy needed to beak 1 mol of a particular covalent bond