HESI A2 Chemistry Test
25 Questions
Step-by-step Answer Explanations
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LATEST UPDATE
, 1. 1. Question
Which of the following reactions is a decomposition reaction?
NaCl+AgNO3→NaNO3+AgCl
CH4+2O2→CO2+2H2O
2H2O→2H2+O2
2H2+O2→2H2O
Answer:
2H2O→2H2+O2
A decomposition reaction is when one substance breaks down into two or more simpler
substances. Think of it like taking apart a LEGO creation into separate pieces.
The general form is:
AB→A+B
2H2O→2H2+O2
This is a decomposition reaction because water (H2O) splits into hydrogen gas (H2) and oxygen
gas (O2). It’s like breaking water apart into its basic building blocks.
Let’s review why the other options are incorrect:
NaCl+AgNO3→NaNO3+AgCl
This is a double replacement reaction, where the parts of two substances switch places. It’s like
swapping partners in a dance.
CH4+2O2→CO2+2H2O
This is a combustion reaction, which is like burning something. Methane (CH4) burns with
oxygen (O2) to produce carbon dioxide (CO2) and water (H2O).
, 2H2+O2→2H2O
This is a synthesis reaction, where two substances, hydrogen (H2) and oxygen (O2), combine to
form water (H2O).
Therefore, the correct answer is 2H2O→2H2+O2 because it’s the only reaction that shows
something breaking down into simpler parts.
2. 2. Question
Express the number 0.00045 in scientific notation.
4.5×10−3
45×10−5
4.5×10−4
4.5×10−2
Answer:
4.5×10−4
Scientific notation is a way to represent very large or very small numbers in a concise form,
using a number between 1 and 10 (the significand) and a power of 10 (the exponent). Here’s a
detailed breakdown for converting 0.00045 to scientific notation:
Step 1:
Start with 0.00045 To put it in scientific notation, we need to move the decimal to make it 4.5 (a
number between 1 and 10). To do this, we move the decimal four places to the right.
Step 2:
Since we moved the decimal four places to the right, we use a negative exponent, which shows
that the original number was small. The final answer is 4.5×10−4.
Let’s review why the other options are incorrect:
4.5×10−3is incorrect because would mean moving the decimal three places, making it 0.0045,
which is too large.
25 Questions
Step-by-step Answer Explanations
Pass Guarantee
LATEST UPDATE
, 1. 1. Question
Which of the following reactions is a decomposition reaction?
NaCl+AgNO3→NaNO3+AgCl
CH4+2O2→CO2+2H2O
2H2O→2H2+O2
2H2+O2→2H2O
Answer:
2H2O→2H2+O2
A decomposition reaction is when one substance breaks down into two or more simpler
substances. Think of it like taking apart a LEGO creation into separate pieces.
The general form is:
AB→A+B
2H2O→2H2+O2
This is a decomposition reaction because water (H2O) splits into hydrogen gas (H2) and oxygen
gas (O2). It’s like breaking water apart into its basic building blocks.
Let’s review why the other options are incorrect:
NaCl+AgNO3→NaNO3+AgCl
This is a double replacement reaction, where the parts of two substances switch places. It’s like
swapping partners in a dance.
CH4+2O2→CO2+2H2O
This is a combustion reaction, which is like burning something. Methane (CH4) burns with
oxygen (O2) to produce carbon dioxide (CO2) and water (H2O).
, 2H2+O2→2H2O
This is a synthesis reaction, where two substances, hydrogen (H2) and oxygen (O2), combine to
form water (H2O).
Therefore, the correct answer is 2H2O→2H2+O2 because it’s the only reaction that shows
something breaking down into simpler parts.
2. 2. Question
Express the number 0.00045 in scientific notation.
4.5×10−3
45×10−5
4.5×10−4
4.5×10−2
Answer:
4.5×10−4
Scientific notation is a way to represent very large or very small numbers in a concise form,
using a number between 1 and 10 (the significand) and a power of 10 (the exponent). Here’s a
detailed breakdown for converting 0.00045 to scientific notation:
Step 1:
Start with 0.00045 To put it in scientific notation, we need to move the decimal to make it 4.5 (a
number between 1 and 10). To do this, we move the decimal four places to the right.
Step 2:
Since we moved the decimal four places to the right, we use a negative exponent, which shows
that the original number was small. The final answer is 4.5×10−4.
Let’s review why the other options are incorrect:
4.5×10−3is incorrect because would mean moving the decimal three places, making it 0.0045,
which is too large.
