Signs of Chemical Reactions
Give one sign of a chemical reaction.
Bubbles of gas
Colour change
Temperature change
Light produced
Solid formed (precipitate)
What is a catalyst?
A substance that speeds up a reaction without being used up
What is a chemical reaction?
When substances react and new substances are formed.
What does rate of reaction mean?
How fast a reaction happens.
In an experiment, what is the independent variable
The variable you change.
When citric acid reacts with sodium hydrogen carbonate, bubbles of gas are released and the reaction becomes cold.
Name one sign of the chemical reaction.
Gas bubbles produced
Temperature decreases (reaction gets colder)
What is an enzyme?
A biological catalyst found in living cells.
What are the substances at the start of a reaction called?
Reactants.
A student added vinegar to large chunks of bicarbonate of soda, but the reaction was slow.
What could they do to speed up the reaction?
Crush the bicarbonate into smaller pieces / powder.
What is the dependent variable?
The variable you measure.
When lead nitrate reacts with potassium iodide, a bright yellow solid forms.
What is this solid called?
A precipitate
In the hydrogen peroxide experiment with potatoes and carrots, which enzyme breaks down hydrogen peroxide?
Catalase.
What are the substances formed at the end of a reaction called?
Products.
Name two ways to speed up a chemical reaction.
Increase temperature
Increase concentration
Increase surface area
Add a catalyst
To find out how temperature affects how fast sugar dissolves.
Identify the independent variable.
Temperature of the water
Why does a temperature change suggest a chemical reaction has taken place?
Energy is released or absorbed during the reaction
Why does the enzyme experiment produce foam?
Oxygen gas is produced.
Name one example of a chemical reaction in everyday life
Respiration
Rusting
Burning
Photosynthesis
Why does crushing a solid speed up a reaction?
It increases surface area so particles collide more often.
In the same experiment, what is the dependent variable?
Time taken for the sugar to dissolve.
Carbon dioxide and water are produced in the citric acid reaction. How could we test for carbon dioxide
Bubble the gas through limewater.
It turns cloudy/milky.
A student investigated how temperature affects the time taken for a Vitamin C tablet to dissolve.
State the expected trend in results
As temperature increases, the tablet dissolves faster.
Ice melting into liquid water is a chemical reaction.
True or False?
False — it is a physical change.
Mixing sodium hydroxide with hydrochloric acid is exothermic.
What does exothermic mean?
Heat/energy is released to the surroundings.
A student carried out an experiment only once.
Suggest two improvements to make it valid
Repeat the experiment
Calculate an average