Chemical reactions Flashcards
Chemical reactions make new ___.
chemicals
Atoms are __ during a chemical reaction, but the number of atoms does not change.
rearranged
Evidence of chemical reactions includes a large __ change, ___ , or a __ change.
temperature
bubbles
colour
Chemical reactions can be represented using.
equations
Do you think it would be easy to get the ingredients back after cooking? Explain your reasoning in terms of a chemical reaction.
It would be impossible to get the ingredients back from the cooked cake. This is because a chemical reaction has taken place between ingredients such as flour, baking powder, sugar, eggs and butter.
A new ___ must be produced for a chemical reaction to take place.
substance
Boiling is a ___ change, not a chemical reaction.
physical
There is a colour change when you add a teabag to a mug of boiling water. Why is this not a chemical reaction?
The chemicals in the tea are dissolving in the water, and dissolving is not a chemical reaction – it is a physical change.
Sodium bicarbonate is also known as __
baking soda.
__ is the chemical name for vinegar.
Ethanoic acid
If you mix ___ and __ , a reaction will occur, where lots of bubbles of carbon dioxide gas form.
vinegar
baking soda
whats the word formula for the reaction of vinegar and baking soda?
sodium bicarbonate + ethanoic acid → sodium ethanoate + water + carbon dioxide
Can you recall the formula for water and carbon dioxide?
The formula for water is H₂O. The formula for carbon dioxide is CO₂.
Physical changes, such as __ , __ and ____, do not make new chemicals. They are usually easy to __ .
melting
boiling
dissolving
reverse
In a chemical reaction, ___ between atoms are broken and made, so the atoms get ___ into new substances.
chemical bonds
rearranged
The simplest kind of chemical reactions involve two ___ reacting together to make a ___ .
elements
compound
Which two elements react together to make the compound sulfur dioxide?
Sulfur and oxygen.
A ___ is a chemical compound containing the element sulfur.
sulfide
What has happened to the total number of atoms during the chemical reactions?
They do not change.
When a chemical reaction happens, ___ is transferred to or from the surroundings.
energy
When energy is transferred to the surroundings, this is called an ___ reaction and usually feels hot.
exothermic
When energy is taken in from the surroundings, this is called an ___ reaction and usually feel cold
endothermic
In a ___ reaction, fuel is burned and reacts with __ to release energy.
combustion
oxygen
___ is the chemical change that takes place inside living cells. Glucose and oxygen are used to release energy that organisms need to live.
Respiration
Reactions that release energy (2)
- combustion
- respiration
Reactions that absorb energy (1)
- photosynthesis
___ absorbs energy from sunlight, allowing plants to make glucose and oxygen from carbon dioxide and water.
Photosynthesis
What happens to the temperature when citric acid and bicarbonate of soda were mixed?
The temperature decreases. We call this an endothermic reaction.
___ are chemical reactions which release energy from the chemicals into the surroundings.
Exothermic reactions
This energy is usually released as heat, so the surroundings get hotter.
Exothermic reactions don’t always release heat, sometimes the energy is released as ___ .
light
Is respiration an exothermic reaction or an endothermic reaction?
Respiration is an exothermic reaction because it releases energy.
What happens when Sodium hydroxide solution is poured into a beaker of hydrochloric acid.
The beaker now contains sodium chloride and water. The temperature on the thermometer has risen, meaning it is an exothermic reaction.
Thermal decomposition reactions are___ because they absorb energy when the chemicals are heated.
endothermic
What happens when sodium carbonate powder is tipped into a beaker of ethanoic acid.
The beaker now contains sodium ethanoate, water and carbon dioxide. The temperature on the thermometer has fallen, meaning it is an endothermic reaction.
When ammonium chloride powder is mixed with barium hydroxide powder and stirred, a chemical reaction takes place. The temperature drops to –14°C.
Is this reaction exothermic or endothermic?
It’s an endothermic reaction.
This is because the temperature of the surroundings decreased.
Exothermic and endothermic reactions that occur at room temperature in the science lab can be investigated using a ___ .
thermometer
How can I increase accuracy when measuring exothermic and endothermic reactions?
Accuracy can be improved by getting a precise value for the room temperature before the experiment begins, and using an insulated polystyrene cup to stop unwanted heat transfers.
Sometimes one result from a set of repeat measurements is very different from the rest of the results. This is called an __ or an ___ result.
outlier
anomalous
Why would it be a good idea to put an insulating lid onto the polystyrene cup when doing this experiment?
It would prevent heat from escaping out of the cup during an exothermic reaction and it would prevent heat from entering the cup in an endothermic reaction.
This makes the results more accurate.
A word equation represents a chemical reaction using the __ of the substances involved. Word equations do not show any __ or __ .
names
chemical symbols
formulae
In a chemical reaction, __ are the substances that react together, and ___ are the substances formed.
reactants
products
__ always take the form, reactants → products. A + sign separates two or more reactants or products.
Word equations
Which of the following processes is easier to reverse or undo?
Melting an ice cube
Burning a piece of wood
Melting and freezing are physical changes, so they are easy to reverse. To reverse this process the water needs to be cooled until it freezes again, probably using a freezer.
It is impossible to reverse the process of burning a piece of wood. This is because it is a chemical reaction.
Summarise the following chemical reaction into a word equation. Sulfuric acid reacts with black powdered copper oxide to make a solution of copper sulfate and water.
Sulfuric acid + copper oxide → copper sulfate + water
Reactants always go first in word equations, and the names of the reactants are separated using __ symbols.
+
In word equations, after the reactants, there is an __ , to show that the chemical reaction has taken place.
arrow, →
In word equations, The __ are written after the arrow, separated by + symbols.
products
When writing chemcial equations, never mix__ and ___ in the same equation.
words
formulas
Words like __ , ___ or __ , are not included in word equations.
powder
solution
gas
Can you spot the three mistakes in this word equation for the reaction taking place in a Bunsen burner?
Methane gas + oxygen = carbon dioxide plus water
The word gas should not be included.
The = symbol should be an arrow → instead.
The word plus should be swapped for a + symbol.
The correct equation is:
methane + oxygen → carbon dioxide + water
The chemicals which react together in a chemical reaction are called ___ .
reactants
A chemical reaction stops when one of the __ but there might be some of the other reactant left over.
reactants runs out,
Chemical reactions are normally __, unlike physical changes which can be reversed.
impossible to reverse
And when the wood in a fire has completely burnt, the burning __, even though there is plenty of oxygen present in the air.
stops
Can you name some differences between a physical change and a chemical reaction?
- Physical changes like melting and dissolving are usually easy to reverse, but chemical reactions are usually impossible to undo.
- Chemical reactions often involve a large energy change, bubbles, or a colour change as new chemical reactions are made.
In a chemical reaction, the ___ are the substances which are formed.
products
When the methane reacts with oxygen in a Bunsen burner, the products are usually __ and.
carbon dioxide
water
When hydrogen reacts with oxygen, water is made. What are the names of the reactants and products in this reaction?
The reactants are hydrogen and oxygen. There is only one product, water.
Here is the word equation for this reaction:
Hydrogen + oxygen → water
___ are a quick way of representing chemical reactions. They show us what atoms are involved and how they are bonded together.
Symbol equations
Symbol equations always take the form, ___ . A + sign separates two or more reactants or products.
reactants → products
__ are used in symbol equations to show whether each chemical is a solid, liquid, gas or solution.
State symbols
In a symbol equation, what symbol is used to show a chemical reaction has taken place?
An arrow → is used.
This goes between the reactants on the left and the products on the right.
In symbol equations, __ and are used to represent elements and compounds,
Chemical symbols
formulae
H₂ is the formula of __
hydrogen
H₂SO₄ is the formula of __
sulfuric acid
Mg is the symbol of magnesium, this is a symbol and not a formula because there are no __
numbers
Some __ elements are made from molecules. For example, hydrogen has a chemical formula of H₂, and oxygen is O₂. The little numbers are called ___ and show how many atoms of that element are present.
non-metal
subscripts