C6 - Rates

What is the rate of a chemical reaction?

• The speed at which the reactants are changed into products

• The temperature at which the reaction occurs

• The color change observed during the reaction

• The amount of catalyst used in the reaction

What equations can we use to calculate the rate of reaction?

• mean rate of reaction = quantity of reactant used / time taken; mean rate of reaction = quantity of product formed / time taken

• mean rate of reaction = time taken / quantity of reactant used; mean rate of reaction = time taken / quantity of product formed

• mean rate of reaction = (quantity of reactant used + quantity of product formed) / time taken

• mean rate of reaction = quantity of reactant used × time taken; mean rate of reaction = quantity of product formed × time taken

What units are used to measure the quantity of reactant or product?

• Mass in grams (if it is a solid), or volume in cm³ (if it is a gas)

• Temperature in Celsius or Kelvin

• Pressure in atmospheres or Pascals

• Time in seconds or minutes

What units can be used to represent the rate of reaction?

• Grams per second (g/s) or cubic centimetres per second (cm³/s)

• Joules per kelvin (J/K)

• Meters per second squared (m/s²)

• Candela per second (cd/s)

What is 'collision theory'?

• Chemical reactions only occur when the reacting particles collide with each other with sufficient energy

• Chemical reactions occur without any interaction between particles

• Collision theory states that all collisions result in chemical reactions

• Collision theory is only applicable to physical changes

What is the 'activation energy'?

• The minimum amount of energy the particles need to collide with to react

• The energy released during a chemical reaction

• The energy required to break all bonds in the reactants

• The energy stored in the products of a reaction

What four factors can affect the rate of reaction?

• Temperature, concentration or pressure, surface area, use of a catalyst

• Volume, density, color, taste

• Mass, shape, odor, solubility

• Light, sound, magnetism, electricity

What happens to the rate of reaction if the temperature is increased?

• Increases

• Decreases

• Remains the same

• Stops completely

Why does the rate of reaction increase if the temperature of the reactants is increased?

• There are more successful collisions because the particles have more energy. There are more frequent collisions because they are moving faster.

• The reactants become heavier and move slower.

• The products absorb all the energy and stop reacting.

• The reaction vessel expands, causing fewer collisions.

What happens to the rate of reaction if concentration or pressure is increased?

• Increases

• Decreases

• Remains the same

• Becomes zero