Chemical Change & Rate of Reaction (Cambridge (CIE) IGCSE Co-ordinated Sciences (Double Award): Chemistry): Flashcards
Exam code: 0654 & 0973
1/420Still learning
Know0
What is a physical change?
Was this flashcard helpful?
Cards in this collection (42)
What is a physical change?
A physical change is a change that does not produce any new chemical substances. It is usually easy to reverse and the substances involved can be easily separated.
State three observable signs that a chemical reaction has taken place.
Signs that a chemical reaction has taken place include:
Colour change
Temperature change
Effervescence (fizzing)
Change of physical state
A smell being produced
Light being given out
Physical changes are usually easy to ______ and the components are relatively easy to ______.
Physical changes are usually easy to reverse and the components are relatively easy to separate.
True or False?
A chemical change always produces a colour change.
False.
A colour change is one possible sign of a chemical reaction, but it does not always occur. Other signs include temperature changes, effervescence, a change in pH or a change of physical state.
How do chemical changes differ from physical changes in terms of the substances present?
Chemical changes produce new chemical substances with very different properties to the reactants.
Physical changes do not produce any new substances at all.
A reaction that releases heat energy to the surroundings is called ______, while one that absorbs heat energy from the surroundings is called ______.
A reaction that releases heat energy to the surroundings is called exothermic, while one that absorbs heat energy from the surroundings is called endothermic.
Define effervescence in the context of chemical reactions.
Effervescence is the fizzing observed during some chemical reactions, caused by the rapid production of a gas. It is a sign that a new substance (the gas) has been formed.
State five factors that can affect the rate of a chemical reaction.
The rate of a chemical reaction can be affected by the concentration of reactants in solution, pressure of reacting gases, surface area of solid reactants, temperature and the presence of a catalyst.
What is a catalyst?
A catalyst is a substance that speeds up the rate of a reaction without being altered or consumed in the reaction. Its mass at the start and end of the reaction remains the same.
Increasing the ______ of a solid reactant increases the rate of reaction. This is equivalent to decreasing the ______ of the solid particles.
Increasing the surface area of a solid reactant increases the rate of reaction. This is equivalent to decreasing the particle size of the solid particles.
True or False?
Using a catalyst in a reaction increases the total amount of product formed.
False.
A catalyst increases the rate of reaction but does not change the total amount of product formed. The reaction reaches completion sooner, but the final yield is the same.
How does increasing temperature affect the rate of a reaction, and what does this look like on a rate graph?
Increasing temperature increases the rate of reaction.
On a graph of product formed against time, the curve at higher temperature has a steeper initial gradient and becomes horizontal sooner, while reaching the same final amount of product.
Increasing the ______ of a gas has the same effect on reaction rate as increasing the ______ of a solution.
Increasing the pressure of a gas has the same effect on reaction rate as increasing the concentration of a solution.
Why is a higher rate of reaction often desirable in industrial processes?
A higher rate of reaction is desirable in industrial processes because it increases the rate of production, making the process more efficient and economically viable.
What is the activation energy of a reaction?
The activation energy is the minimum energy that colliding particles must have in order to react and form products.
State the two conditions that must be met for a collision between reactant particles to be successful.
For a collision to be successful, the particles must collide with sufficient energy (equal to or greater than the activation energy) and with the correct orientation to allow bonds to break and reform.
Collision theory states that particles must ______ with ______ energy in order to react and form products.
Collision theory states that particles must collide with sufficient energy in order to react and form products.
True or False?
Every collision between reactant particles results in a chemical reaction.
False.
Only successful collisions lead to a reaction. A collision is unsuccessful if the particles do not have sufficient energy to exceed the activation energy or do not collide with the correct orientation.
Why does increasing the kinetic energy of particles increase the rate of reaction?
Increasing the kinetic energy of particles means a greater proportion of collisions have energy that exceeds the activation energy. Particles also move faster, so collisions are more frequent, resulting in more successful collisions per unit of time.
An ______ collision results in reactant particles rearranging to form products, while an ______ collision results in particles simply bouncing off each other.
A successful collision results in reactant particles rearranging to form products, while an unsuccessful collision results in particles simply bouncing off each other.
How does the activation energy of a reaction affect the rate at which it proceeds?
A higher activation energy means fewer collisions have sufficient energy to react, so a smaller proportion of collisions are successful and the reaction proceeds more slowly.
How does increasing concentration increase the rate of reaction? Use collision theory in your answer.
Increasing concentration means there are more reactant particles per unit volume. This increases the frequency of collisions, leading to more successful collisions per second and a higher rate of reaction.
A catalyst increases the rate of reaction by providing a different reaction pathway with a ______ activation energy, so a greater proportion of particles have energy ______ the activation energy.
A catalyst increases the rate of reaction by providing a different reaction pathway with a lower activation energy, so a greater proportion of particles have energy exceeding the activation energy.
True or False?
Increasing concentration, surface area and temperature all increase the rate of reaction by increasing the energy of collisions.
False.
Only temperature directly increases the energy of collisions. Increasing concentration and surface area increase the frequency of collisions but do not affect the energy of individual collisions.
Why does increasing the surface area of a solid reactant increase the rate of reaction?
Increasing surface area exposes more reactant particles to the other reactant. This increases the frequency of collisions between particles, leading to more successful collisions per second.
Increasing the pressure of a reacting gas increases the rate of reaction because the same number of particles are contained in a ______ volume, causing more ______ per second.
Increasing the pressure of a reacting gas increases the rate of reaction because the same number of particles are contained in a smaller volume, causing more collisions per second.
How does increasing temperature affect both the frequency and energy of particle collisions?
Increasing temperature gives particles more kinetic energy. This increases both the frequency of collisions (particles move faster) and the proportion of collisions that exceed the activation energy, so the rate of reaction increases significantly.
What is meant by the term 'biological catalyst'?
A biological catalyst is an enzyme, a substance produced by living organisms that speeds up specific reactions in cells.
State three properties that can be monitored to measure the rate of a chemical reaction in the laboratory.
Three properties that can be monitored are colour change, loss in mass and volume of gas produced. The changing property is taken to be proportional to the concentration of the reactant or product.
In the sodium thiosulfate and hydrochloric acid experiment, the rate is measured by timing how long it takes for a ______ drawn under the flask to become invisible due to the formation of a ______ precipitate.
In the sodium thiosulfate and hydrochloric acid experiment, the rate is measured by timing how long it takes for a cross drawn under the flask to become invisible due to the formation of a sulfur precipitate.
True or False?
Measuring mass loss on a balance is a suitable method for monitoring the rate of a reaction that produces hydrogen gas.
False.
Mass loss measurement is not suitable for hydrogen gas because hydrogen has a very low relative molecular mass (Mr), so the loss in mass is too small to measure accurately.
How is the volume of gas produced used to investigate the effect of surface area on the rate of reaction between magnesium and hydrochloric acid?
The volume of gas produced in a fixed time is measured using downward displacement of water. The experiment is repeated with different sizes of magnesium pieces (keeping the total mass constant) and the volumes are compared to determine the effect of surface area.
In an investigation into the effect of a catalyst, manganese(IV) oxide is added to ______ ______ solution and the volume of ______ gas collected is measured over time.
In an investigation into the effect of a catalyst, manganese(IV) oxide is added to hydrogen peroxide solution and the volume of oxygen gas collected is measured over time.
Why is cotton wool placed in the mouth of the flask when measuring reaction rate by mass loss?
Cotton wool is placed in the mouth of the flask to allow gas to escape (so the mass loss can be measured) while preventing any solid or liquid material from being ejected from the flask if the reaction is vigorous.
What does 'downward displacement of water' mean in the context of gas collection?
Downward displacement of water is a method of collecting gas in which gas produced by a reaction travels through a delivery tube into an inverted measuring cylinder filled with water. The gas displaces the water downward, allowing the volume to be read.
At what point during a reaction is the rate at its greatest, and what does this look like on a graph of product formed against time?
The rate is greatest at the start of the reaction, when reactant concentrations are highest. On a graph this appears as the steepest gradient at the beginning, which becomes less steep as the reaction progresses.
On a graph of volume of gas produced against time, the reaction is complete when the line becomes ______. At this point the rate of reaction is ______.
On a graph of volume of gas produced against time, the reaction is complete when the line becomes horizontal. At this point the rate of reaction is zero.
True or False?
Increasing the concentration of the excess reactant increases the total amount of product formed.
False.
The total amount of product formed is determined by the limiting reactant. Increasing the amount of the reactant in excess does not change the final amount of product.
What is a tangent, and why is it drawn on a rate of reaction graph?
A tangent is a straight line that touches a curve at a single point without crossing it.
It is drawn on a rate of reaction graph to find the gradient at that point, which gives the rate of reaction at that moment in time.
How does increasing concentration affect the shape of a product-versus-time graph?
Increasing concentration produces a steeper initial gradient on the graph, and the curve reaches its final (horizontal) level sooner. If only the concentration of the limiting reactant is increased, the final level reached is also higher.
The rate of reaction at a given point is calculated as the ______ of the tangent drawn to the curve at that point, using the formula: rate = change in ______ divided by change in ______.
The rate of reaction at a given point is calculated as the gradient of the tangent drawn to the curve at that point, using the formula: rate = change in y divided by change in x.
Why does the rate of reaction decrease as a reaction progresses?
The rate decreases as the reaction progresses because reactants are being used up, so their concentration falls. Fewer reactant particles per unit volume means fewer collisions per second and fewer successful collisions.
Sign up to unlock flashcards
or